Modifying the way GAC elimination works so it will work in MSBuild (#540)

XBuild adds extra semi-colons to the string when serializing. I remove them via split to make MSBuild work.

msbuild/Xamarin.Mac.Tasks/Xamarin.Mac.Common.targets

@@ -66,6 +66,7 @@ Copyright (C) 2014 Xamarin. All rights reserved.
 	<!-- Do not resolve from the GAC under any circumstances in Mobile or XM45 -->
 	<PropertyGroup Condition="(('$(TargetFrameworkIdentifier)' != 'Xamarin.Mac' And '$(UseXamMacFullFramework)' == 'true') Or '$(TargetFrameworkIdentifier)' == 'Xamarin.Mac') And !$(MonoBundlingExtraArgs.Contains('--allow-unsafe-gac-resolution'))" >
 		<AssemblySearchPaths>$([System.String]::Copy('$(AssemblySearchPaths)').Replace('{GAC}',''))</AssemblySearchPaths>
+		<AssemblySearchPaths Condition="'$(MSBuildRuntimeVersion)' != ''">$(AssemblySearchPaths.Split(';'))</AssemblySearchPaths>
 	</PropertyGroup>
 
 	<PropertyGroup>