Using Macports' gcc8 to build C programs and libraries

[Sean Lake]

Hello Macports Users:

I have a collection of libraries I use in running simulations, and I
recently moved from Fink to Macports to support a Mojave machine. I'm
trying to build the libraries using my installed gcc8, but I'm running
in to errors like:

In file included from MWReddening.c:1:
/opt/local/lib/gcc8/gcc/x86_64-apple-darwin18/8.3.0/include-fixed/math.h:45:10:fatal
error: sys/cdefs.h: No such file or directory
 #include <sys/cdefs.h>
          ^~~~~~~~~~~~~

Looking for similar errors on the web, I get pages like this

https://stackoverflow.com/questions/31045721/c-compiler-error-cdefs-h-not-found

that recommend installing a libc package. Will a similar solution work
in Macports? If so, which package(s)? If not, will modifying my CFLAGS
and LDFLAGS suffice? Currently, I have included "-I/opt/local/include"
in CFLAGS and "-L/opt/local/lib" in LDFLAGS, but that's obviously not
enough (or wrong).

Thanks,
Sean Lake