If I try to take a big hammer to it by commenting out all the run_tests() function code in apitest_main.cpp, I get the following out (sorry, it is ugly):
$ make -k
[ 2%] Built target sixseries
[ 4%] Built target tritri
[ 4%] Built target clipper
[ 5%] Built target wavedragEL
[ 11%] Built target pinocchio
[ 27%] Built target Angelscript
[ 38%] Built target util
[ 39%] Built target xmlvsp
[ 67%] Built target geom_core
[ 75%] Built target cfd_mesh
[ 76%] Built target geom_api
Scanning dependencies of target apitest
[ 76%] Building CXX object src/vsp/CMakeFiles/apitest.dir/apitest_main.cpp.o
[ 77%] Linking CXX executable apitest
../cfd_mesh/libcfd_mesh.a(SurfaceIntersectionMgr.cpp.o): In function `SurfaceIntersectionSingleton::WriteSTEPFile(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int, double, bool, bool, bool, bool, bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int)':
SurfaceIntersectionMgr.cpp:(.text+0xfd49): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../cfd_mesh/libcfd_mesh.a(NURBS.cpp.o): In function `NURBS_Curve::WriteSTEPEdge(STEPutil*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool)':
NURBS.cpp:(.text+0x955): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakePlane(vec3d, vec3d, vec3d, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
CADutil.cpp:(.text+0x3403): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::RepresentUntrimmedSurfs(std::vector<SdaiB_spline_surface_with_knots*, std::allocator<SdaiB_spline_surface_with_knots*> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
CADutil.cpp:(.text+0x35d9): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakeCurve(std::vector<vec3d, std::allocator<vec3d> >, int const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, bool, double)':
CADutil.cpp:(.text+0x39bd): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o):CADutil.cpp:(.text+0x481b): more undefined references to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)' follow
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::WriteFile(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
CADutil.cpp:(.text+0x54ba): undefined reference to `STEPfile::WriteExchangeFile(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int, int, int)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::STEPutil(int const&, double const&)':
CADutil.cpp:(.text+0x55d5): undefined reference to `STEPfile::STEPfile(Registry&, InstMgr&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakeSurfaceCurve(std::vector<vec3d, std::allocator<vec3d> >, int const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, double)':
CADutil.cpp:(.text+0x60a8): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakeSurf(eli::geom::surface::piecewise<eli::geom::surface::bezier, double, (unsigned short)3, eli::util::tolerance<double> >&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, double)':
CADutil.cpp:(.text+0x7c3a): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
collect2: error: ld returned 1 exit status
make[2]: *** [src/vsp/apitest] Error 1
make[2]: Target `src/vsp/CMakeFiles/apitest.dir/build' not remade because of errors.
make[1]: *** [src/vsp/CMakeFiles/apitest.dir/all] Error 2
[ 77%] Linking CXX executable vspscript
../cfd_mesh/libcfd_mesh.a(SurfaceIntersectionMgr.cpp.o): In function `SurfaceIntersectionSingleton::WriteSTEPFile(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int, double, bool, bool, bool, bool, bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int)':
SurfaceIntersectionMgr.cpp:(.text+0xfd49): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../cfd_mesh/libcfd_mesh.a(NURBS.cpp.o): In function `NURBS_Curve::WriteSTEPEdge(STEPutil*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool)':
NURBS.cpp:(.text+0x955): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakePlane(vec3d, vec3d, vec3d, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
CADutil.cpp:(.text+0x3403): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::RepresentUntrimmedSurfs(std::vector<SdaiB_spline_surface_with_knots*, std::allocator<SdaiB_spline_surface_with_knots*> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
CADutil.cpp:(.text+0x35d9): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakeCurve(std::vector<vec3d, std::allocator<vec3d> >, int const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, bool, double)':
CADutil.cpp:(.text+0x39bd): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o):CADutil.cpp:(.text+0x481b): more undefined references to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)' follow
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::WriteFile(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
CADutil.cpp:(.text+0x54ba): undefined reference to `STEPfile::WriteExchangeFile(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, int, int, int)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::STEPutil(int const&, double const&)':
CADutil.cpp:(.text+0x55d5): undefined reference to `STEPfile::STEPfile(Registry&, InstMgr&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakeSurfaceCurve(std::vector<vec3d, std::allocator<vec3d> >, int const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, double)':
CADutil.cpp:(.text+0x60a8): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
../util/libutil.a(CADutil.cpp.o): In function `STEPutil::MakeSurf(eli::geom::surface::piecewise<eli::geom::surface::bezier, double, (unsigned short)3, eli::util::tolerance<double> >&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, double)':
CADutil.cpp:(.text+0x7c3a): undefined reference to `SDAI_String::SDAI_String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
collect2: error: ld returned 1 exit status
make[2]: *** [src/vsp/vspscript] Error 1
make[2]: Target `src/vsp/CMakeFiles/vspscript.dir/build' not remade because of errors.
make[1]: *** [src/vsp/CMakeFiles/vspscript.dir/all] Error 2
[ 92%] Built target vspaero
[ 95%] Built target vspslicer
[ 95%] Built target vsp_swig_compilation
[ 96%] Built target _vsp
make[1]: Target `all' not remade because of errors.