Set MACOS_VERSION and WATCHOS5_VERSION in the Mono SDKs config

To make sure we correctly propagate the values from xamarin-macios.

builds/Makefile

@@ -124,6 +124,8 @@ SDK_ARGS= \
 	IOS_VERSION=$(IOS_SDK_VERSION) IOS_VERSION_MIN=$(MIN_IOS_SDK_VERSION) \
 	TVOS_VERSION=$(TVOS_SDK_VERSION) TVOS_VERSION_MIN=$(MIN_TVOS_SDK_VERSION) \
 	WATCHOS_VERSION=$(WATCH_SDK_VERSION) WATCHOS_VERSION_MIN=$(MIN_WATCHOS_SDK_VERSION) \
+	WATCHOS5_VERSION=$(WATCH_SDK_VERSION) WATCHOS5_VERSION_MIN=$(MIN_WATCHOS_SDK_VERSION) \
+	MACOS_VERSION=$(OSX_SDK_VERSION) MACOS_VERSION_MIN=$(MIN_OSX_SDK_VERSION)
 	IGNORE_PROVISION_LLVM=1
 
 ifdef DISABLE_DOWNLOAD_LLVM