Fix GCMetadaPrinter::finishAssembly not executed, patch by Yiannis Tsiouris.

Due to the execution order of doFinalization functions, the GC information were
deleted before AsmPrinter::doFinalization was executed. Thus, the
GCMetadataPrinter::finishAssembly was never called.

The patch fixes that by moving the code of the GCInfoDeleter::doFinalization to
Printer::doFinalization.

llvm-svn: 175528