Ignore stderr from xcrun.

Author: jakepetroules

Makefile

@@ -22,7 +22,7 @@ test:
 
 ci:
 	for i in {7..11} ; do \
-		if xcrun --sdk "macosx10.$$i" --show-sdk-path ; then \
+		if xcrun --sdk "macosx10.$$i" --show-sdk-path 2> /dev/null ; then \
 			xcodebuild -sdk "macosx10.$$i" -scheme Distribution -configuration Debug test ; \
 		fi ; \
 	done