Fix Matter.framework compilation when -Wundef is enabled. (#28424)

Apparently we have some framework consumers that set -Wundef, so fail when
MTR_ENABLE_PROVISIONAL is not defined.

Author: bzbarsky-apple

src/darwin/Framework/CHIP/MTRDefines.h

@@ -53,7 +53,7 @@
 #define MTR_NEWLY_AVAILABLE
 #endif
 
-#if MTR_ENABLE_PROVISIONAL
+#if defined(MTR_ENABLE_PROVISIONAL) && MTR_ENABLE_PROVISIONAL
 #define MTR_PROVISIONALLY_AVAILABLE MTR_NEWLY_AVAILABLE
 #else
 #define MTR_PROVISIONALLY_AVAILABLE NS_UNAVAILABLE MTR_HIDDEN