sag-7.2 fails to build on Arch linux

[pong]

I aware of the problem of Singular and set CXXFLAGS to -std=gnu++98. The compliation got pass Singular all the way to almost the end, but giving me the follow. I'm not even sure which package(s) it is complaning (sagelib?). And it doesn't indicate a log file to look at...
Any help?


/home/pong/sage-7.2/src/build/cythonized/sage/matrix/matrix_modn_dense_double.cpp: In function ‘PyObject* __pyx_f_4sage_6matrix_24matrix_modn_dense_double_linbox_charpoly(__pyx_t_4sage_6matrix_24matrix_modn_dense_double_celement, Py_ssize_t, __pyx_t_4sage_6matrix_24matrix_modn_dense_double_celement*)’:
/home/pong/sage-7.2/src/build/cythonized/sage/matrix/matrix_modn_dense_double.cpp:5465:35: warning: comparison between
signed and unsigned integer expressions [-Wsign-compare]
     for (__pyx_t_7 = 0; __pyx_t_7 < __pyx_t_6; __pyx_t_7+=1) {
                         ~~~~~~~~~~^~~~~~~~~~~
make[2]: *** [Makefile:953: sagelib] Error 2
make[2]: Leaving directory '/home/pong/sage-7.2/build/make'
make[1]: *** [Makefile:826: all] Error 2
make[1]: Leaving directory '/home/pong/sage-7.2/build/make'

real    147m20.451s
user    140m41.229s
sys     5m47.893s
***************************************************************
Error building Sage.

The following package(s) may have failed to build (not necessarily
during this run of 'make all'):

The build directory may contain configuration files and other potentially
helpful information. WARNING: if you now run 'make' again, the build
directory will, by default, be deleted. Set the environment variable
SAGE_KEEP_BUILT_SPKGS to 'yes' to prevent this.

make: *** [Makefile:18: all] Error 1

[pong]

Now I think it is related to the LinBox header but I don't know enough to understand the hint given by leif in this post:

"So far I've successfully built Sage 7.2 with GCC 6.1 and the above 
changes, except for some Sage library modules which include LinBox 
headers, and hence have to be built with '-std=gnu++98', too." 

How do I build those headers with '-std=gnu++98'?