As more footnote, I built ./pbdSLAP/inst/test_intface/intface and its output is simply
"Add_". That is the default for CDEFS, so I assume I don't need to add
a different definition for the CDEFS flag.
And here are some definitions on my system:
Erikas-MBP-2:~ erika$ echo $PATH
/opt/local/bin:/opt/local/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin
Erikas-MBP-2:test_intface erika$ gfortran -v
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/opt/local/libexec/gcc/x86_64-apple-darwin15/5.2.0/lto-wrapper
Target: x86_64-apple-darwin15
Configured with: /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc5/gcc5/work/gcc-5.2.0/configure --prefix=/opt/local --build=x86_64-apple-darwin15 --enable-languages=c,c++,objc,obj-c++,lto,fortran,java --libdir=/opt/local/lib/gcc5 --includedir=/opt/local/include/gcc5 --infodir=/opt/local/share/info --mandir=/opt/local/share/man --datarootdir=/opt/local/share/gcc-5 --with-local-prefix=/opt/local --with-system-zlib --disable-nls --program-suffix=-mp-5 --with-gxx-include-dir=/opt/local/include/gcc5/c++/ --with-gmp=/opt/local --with-mpfr=/opt/local --with-mpc=/opt/local --with-isl=/opt/local --enable-stage1-checking --disable-multilib --enable-lto --enable-libstdcxx-time --with-as=/opt/local/bin/as --with-ld=/opt/local/bin/ld --with-ar=/opt/local/bin/ar --with-bugurl=
https://trac.macports.org/newticket --with-pkgversion='MacPorts gcc5 5.2.0_0'
Thread model: posix
gcc version 5.2.0 (MacPorts gcc5 5.2.0_0)
Erikas-MBP-2:~ erika$ /opt/local/bin/gfortran-4.8 -v
Using built-in specs.
COLLECT_GCC=/opt/local/bin/gfortran-4.8
COLLECT_LTO_WRAPPER=/opt/local/gfortran-4.8/bin/../libexec/gcc/x86_64-apple-darwin13/4.8.2/lto-wrapper
Target: x86_64-apple-darwin13
Configured with: ../gcc-4.8.2/configure --prefix=/usr/local/gfortran --with-gmp=/Users/fx/devel/gcc/deps-static/x86_64 --enable-languages=c,c++,fortran,objc,obj-c++ --build=x86_64-apple-darwin13
Thread model: posix
gcc version 4.8.2 (GCC)