git-compat-util: fix NO_OPENSSL on current macOS

b195aa0 (git-compat-util: suppress unavoidable Apple-specific
deprecation warnings, 2014-12-16) started to define
__AVAILABILITY_MACROS_USES_AVAILABILITY in git-compat-util.h.  On
current versions it is already defined (e.g. on macOS 14.4.1).  Undefine
it before redefining it to avoid a compilation error.

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rscharfe

git-compat-util.h

@@ -358,6 +358,7 @@ char *gitdirname(char *);
 
 #ifndef NO_OPENSSL
 #ifdef __APPLE__
+#undef __AVAILABILITY_MACROS_USES_AVAILABILITY
 #define __AVAILABILITY_MACROS_USES_AVAILABILITY 0
 #include <AvailabilityMacros.h>
 #undef DEPRECATED_ATTRIBUTE