Removes memory leak of ASTContext and TargetMachine. When DisableFree is turned on, it intentionally leaks these instances as they can be trivially deallocated. This patch turns this off and delete Parser instance early so that they will not reference dangling pargma headers.
Asan shouldn't detect these as leaks, since burypointer is called for them. But, most likely, we have reached number of leaks exceeding kGraveYardMaxSizethese and they start to get reported.