Well you could do this
Code:
$ gcc -M foo.c
foo.o: foo.c /usr/include/stdio.h /usr/include/features.h \
/usr/include/x86_64-linux-gnu/bits/predefs.h \
/usr/include/x86_64-linux-gnu/sys/cdefs.h \
/usr/include/x86_64-linux-gnu/bits/wordsize.h \
/usr/include/x86_64-linux-gnu/gnu/stubs.h \
/usr/include/x86_64-linux-gnu/gnu/stubs-64.h \
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include/stddef.h \
/usr/include/x86_64-linux-gnu/bits/types.h \
/usr/include/x86_64-linux-gnu/bits/typesizes.h /usr/include/libio.h \
/usr/include/_G_config.h /usr/include/wchar.h \
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include/stdarg.h \
/usr/include/x86_64-linux-gnu/bits/stdio_lim.h \
/usr/include/x86_64-linux-gnu/bits/sys_errlist.h \
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include-fixed/limits.h \
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include-fixed/syslimits.h \
/usr/include/limits.h /usr/include/x86_64-linux-gnu/bits/posix1_lim.h \
/usr/include/x86_64-linux-gnu/bits/local_lim.h \
/usr/include/linux/limits.h \
/usr/include/x86_64-linux-gnu/bits/posix2_lim.h
Or this
Code:
$ gcc -E foo.c | awk '/^#/ && $3 ~ "/" { print $3 }' | sort -u
"/usr/include/features.h"
"/usr/include/_G_config.h"
"/usr/include/libio.h"
"/usr/include/limits.h"
"/usr/include/linux/limits.h"
"/usr/include/stdio.h"
"/usr/include/wchar.h"
"/usr/include/x86_64-linux-gnu/bits/local_lim.h"
"/usr/include/x86_64-linux-gnu/bits/posix1_lim.h"
"/usr/include/x86_64-linux-gnu/bits/posix2_lim.h"
"/usr/include/x86_64-linux-gnu/bits/predefs.h"
"/usr/include/x86_64-linux-gnu/bits/stdio_lim.h"
"/usr/include/x86_64-linux-gnu/bits/sys_errlist.h"
"/usr/include/x86_64-linux-gnu/bits/types.h"
"/usr/include/x86_64-linux-gnu/bits/typesizes.h"
"/usr/include/x86_64-linux-gnu/bits/wordsize.h"
"/usr/include/x86_64-linux-gnu/gnu/stubs-64.h"
"/usr/include/x86_64-linux-gnu/gnu/stubs.h"
"/usr/include/x86_64-linux-gnu/sys/cdefs.h"
"/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include-fixed/limits.h"
"/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include-fixed/syslimits.h"
"/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include/stdarg.h"
"/usr/lib/gcc/x86_64-linux-gnu/4.6.1/include/stddef.h"
What's the chance that you're using some other compiler, but didn't think it was worth mentioning at the time.