Sorry if I’m unclear about you’re question, but I’m assuming that you’re seeing an error like the following?
% pgcc flt_max.c -I/usr/lib/gcc/x86_64-redhat-linux/4.8.5/include/
PGC-S-0039-Use of undeclared variable __FLT_MAX__ (flt_max.c: 6)
PGC/x86-64 Linux 19.10-0: compilation completed with severe errors
The problem here, is the GNU 4.8.5 float.h header files presume “FLT_MAX” gets predefined by the compiler but pgcc doesn’t predefine it. Instead, we ship our own “float.h” including it before the system float.h. However, if you put the GNU include file path on the compile line, the GNU float.h will get included first, so FLT_MAX isn’t defined.
Either don’t explicitly add the include path to the GNU headers (the path will get implicitly added in the correct order), or include the the path to the PGI version first.
% pgcc flt_max.c -I/opt/pgi/pgi-19.10/linux86-64-llvm/19.10/include-gcc48 -I/usr/lib/gcc/x86_64-redhat-linux/4.8.5/include/
Hope this helps,