[msbuild] Fix copy/paste error from #11196 (#11206)

Not sure how I could mess up a copy/paste between file - but I succeeded
to create a subtle bug (would have expected it more crash happy)

Fix issue #11151

msbuild/Xamarin.Shared/Xamarin.Shared.targets

@@ -1442,7 +1442,7 @@ Copyright (C) 2018 Microsoft. All rights reserved.
 			Condition="'$(IsMacEnabled)' == 'true' And '$(_NoSymbolStrip)' == 'false' And '$(IsAppExtension)' == 'false'"
 			Executable="$(_NativeExecutable)"
 			IsFramework="false"
-			SymbolFile=""
+			SymbolFile="$(_MtouchSymbolsList)"
 		>
 		</SymbolStrip>