Get gcc Hidden Macro Definition

> touch /tmp/x.c
> gcc -E -dM -c /tmp/x.c

#define __linux__ 1
#define linux 1
#define __i386__ 1
#define __i386 1
#define __GNUC_MINOR__ 95
#define i386 1
#define __unix 1
#define __unix__ 1
#define __GNUC__ 2
#define __linux 1
#define __ELF__ 1
#define unix 1