MC: loosen an overzealous assertion

Permit active macro expansions when terminating the assembler if there were
errors during the expansion.  This would only trigger on invalid input when
built with assertions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209309 91177308-0d34-0410-b5e6-96231b3b80d8
Use cast<> instead of unchecked dyn_cast

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209310 91177308-0d34-0410-b5e6-96231b3b80d8
DebugInfo: Simplify subprogram declaration creation/references and accidentally refix PR11300.

Also simplifies the linkage name handling a little too.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209311 91177308-0d34-0410-b5e6-96231b3b80d8