Fix contrib/libs/zlib build with GCC 4.
It is needed for BUILD_APACHE_BUNDLE task that runs on Ubuntu Precise.
Note: mandatory check (NEED_CHECK) was skipped
@@ -431,11 +431,15 @@ typedef uLong FAR uLongf;
typedef unsigned long z_crc_t;
#endif
-#if __has_include(<unistd.h>)
+#ifdef __GNUC__
+# define Z_HAVE_UNISTD_H
+#elif __has_include(<unistd.h>)
# define Z_HAVE_UNISTD_H
#endif
-#if __has_include(<stdarg.h>)
+#ifdef __GNUC__
+# define Z_HAVE_UNISTD_H
+#elif __has_include(<stdarg.h>)
# define Z_HAVE_STDARG_H
#endif
