How to list all the included header files in a C program

For a simple C program:

#include <stdlib.h>
#include <stdio.h>

int
main(int argc, char **argc)
{
    printf("foo\n");
    return (0);
}

We can use gcc's preprocessor directive and with a little shell processing we get:

$ gcc -E foo.c | grep include | cut -d'"' -f2 | sort | uniq
/usr/include/alloca.h
/usr/include/endian.h
/usr/include/features.h
/usr/include/_G_config.h
/usr/include/libio.h
/usr/include/stdc-predef.h
/usr/include/stdio.h
/usr/include/stdlib.h
/usr/include/time.h
/usr/include/wchar.h
/usr/include/x86_64-linux-gnu/bits/byteswap-16.h
/usr/include/x86_64-linux-gnu/bits/byteswap.h
/usr/include/x86_64-linux-gnu/bits/endian.h
/usr/include/x86_64-linux-gnu/bits/pthreadtypes.h
/usr/include/x86_64-linux-gnu/bits/select.h
/usr/include/x86_64-linux-gnu/bits/sigset.h
/usr/include/x86_64-linux-gnu/bits/stdio_lim.h
/usr/include/x86_64-linux-gnu/bits/stdlib-float.h
/usr/include/x86_64-linux-gnu/bits/sys_errlist.h
/usr/include/x86_64-linux-gnu/bits/time.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/waitflags.h
/usr/include/x86_64-linux-gnu/bits/waitstatus.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/include/x86_64-linux-gnu/sys/select.h
/usr/include/x86_64-linux-gnu/sys/sysmacros.h
/usr/include/x86_64-linux-gnu/sys/types.h
/usr/lib/gcc/x86_64-linux-gnu/4.8/include/stdarg.h
/usr/lib/gcc/x86_64-linux-gnu/4.8/include/stddef.h<.code>