gcc -dM -E - < /dev/null

bob@bob-fedora:~/trunk/software$ gcc --version
gcc (GCC) 4.7.2 20121109 (Red Hat 4.7.2-8)
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

bob@bob-fedora:~/trunk/software$ gcc -std=gnu11 -dM -E - < /dev/null | grep STDC
#define __STDC_HOSTED__ 1
#define __STDC_UTF_16__ 1
#define __STDC_VERSION__ 201112L
#define __GNUC_STDC_INLINE__ 1
#define __STDC_UTF_32__ 1
#define __STDC__ 1

#ifdef __STDC_NO_VLA__
#error Your compiler does not support VLAs! Please use a supported compiler.
#endif

#ifndef __STDC_NO_VLA__
// code using variable length arrays
#else
// fallback code for when they are not supported
#endif