safe-alloc: Remove unused code

[Bruno Haible]

The __GNUC_PREREQ macro definition in lib/safe-alloc.h is not used any more
since 2020-05-02.


2020-08-06  Bruno Haible  <bruno@clisp.org>

        safe-alloc: Remove unused code.
        * lib/safe-alloc.h (__GNUC_PREREQ): Remove macro.

diff --git a/lib/safe-alloc.h b/lib/safe-alloc.h
index 58970bd..9bf1eca 100644
--- a/lib/safe-alloc.h
+++ b/lib/safe-alloc.h
@@ -22,15 +22,6 @@
 
 # include <stdlib.h>
 
-#ifndef __GNUC_PREREQ
-# if defined __GNUC__ && defined __GNUC_MINOR__
-#  define __GNUC_PREREQ(maj, min)                                       \
-  ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
-# else
-#  define __GNUC_PREREQ(maj, min) 0
-# endif
-#endif
-
 /* Don't call these directly - use the macros below */
 int
 safe_alloc_alloc_n (void *ptrptr, size_t size, size_t count, int zeroed)