test/libmpv_lifetime: don't re-define ASAN macro

test/libmpv_lifetime.c

@@ -5,11 +5,14 @@
 
 #include <libmpv/client.h>
 
+// detect enabled ASAN on gcc & clang
+#ifndef __SANITIZE_ADDRESS__
 #if defined(__has_feature)
 #if __has_feature(address_sanitizer)
 #define __SANITIZE_ADDRESS__
 #endif
 #endif
+#endif
 
 #ifdef __SANITIZE_ADDRESS__
 #include <sanitizer/lsan_interface.h>