Fix GH-20002: build on BSD with MSAN

The #if to have instrumented versions of strlcpy and strlcat was too
inclusive, and defined them even on *BSD that indeed have those already
defined, resulting in "duplicate symbol" at linking.

Author: outtersg

Zend/zend_string.c

@@ -502,6 +502,9 @@ ZEND_API zend_string *zend_string_concat3(
 
 /* strlcpy and strlcat are not intercepted by msan, so we need to do it ourselves. */
 #if __has_feature(memory_sanitizer)
+/* apply a simple heuristic to tell if the platform needs it,
+ * see https://github.com/php/php-src/issues/20002 */
+#if !defined(__FreeBSD__) && !defined(__NetBSD__) && !defined(__APPLE__)
 static size_t (*libc_strlcpy)(char *__restrict, const char *__restrict, size_t);
 size_t strlcpy(char *__restrict dest, const char *__restrict src, size_t n)
 {
@@ -523,3 +526,4 @@ size_t strlcat (char *__restrict dest, const char *restrict src, size_t n)
 	return result;
 }
 #endif
+#endif