Bug#57994: Compiler flag change build error : my_redel.c

Use __builtin_stpcpy only if the system supports stpcpy.
This is necessary as in some cases a call to stpcpy will
be emitted if the built-in can not optimized.

include/m_string.h:
  The expansion of stpcpy (in glibc) causes warnings if the
  return value of strmov is not being used. Since stpcpy is
  a GNU extension and the expansion ends up using a built-in
  provided by GCC, use the compiler provided built-in directly
  when possible. Nonetheless, the C library must have stpcpy
  as a call be emitted if the built-in can not optimized.

include/m_string.h

@@ -73,8 +73,8 @@ extern "C" {
 extern void *(*my_str_malloc)(size_t);
 extern void (*my_str_free)(void *);
 
-#if MY_GNUC_PREREQ(3, 4)
-#define strmov(dest, src) __builtin_stpcpy(dest, src)
+#if defined(HAVE_STPCPY) && MY_GNUC_PREREQ(3, 4)
+#define strmov(A,B) __builtin_stpcpy((A),(B))
 #elif defined(HAVE_STPCPY)
 #define strmov(A,B) stpcpy((A),(B))
 #ifndef stpcpy