safe-alloc.h uses __GNUC_PREREQ without defining it

[Tom G. Christensen]

Building the latest snapshot on sparc-sun-solaris2.6 fails:
In file included from safe-alloc.c:27:
safe-alloc.h:30:21: error: missing binary operator before token "("
make[4]: *** [safe-alloc.o] Error 1

It seems __GNUC_PREREQ is used undefined at safe-alloc.h:30.

-tgc