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, for some reason, these leaks got complained several times by asan builtbots.