Add the Microsoft.CSharp.dll assembly back into the unityaot profile

This assembly is in the old unityaot profile, we should have it in
after the Mono upgrade.

mcs/class/Makefile

@@ -199,7 +199,7 @@ orbis_dirs_parallel := \
 	$(filter-out Microsoft.CSharp Mono.Data.Sqlite,$(mobile_common_dirs_parallel))
 
 unityaot_dirs_parallel := \
-	$(filter-out Microsoft.CSharp,$(mobile_common_dirs_parallel))
+	$(mobile_common_dirs_parallel)
 
 xammac_4_5_dirs_parallel := \
 	Mono.Security \