[PATCH] Correct __GNUC_PREREQ for __const__ and __noreturn__ attributes.

[Kang-Che Sung]

To be precise, this correctly parses in gcc-2.7.2 according to my testing:

void __attribute__((__noreturn__)) f(void) {  exit(1); }

But this will not until gcc-2.8.0:

__attribute__((__noreturn__)) void f(void) { exit(1); }

Unfortunately the former way is not compatible with C11's _Noreturn syntax.
I mean I can't just "#define _Noreturn __attribute__((__noreturn__))" and
expect it work.

I guess that's it.