MC: Tidy up.

Clean up some simple code quality issues. Bring internal naming
conventions up to current standard, fix inconsistent formatting, and
tidy up a couple of odd contructs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191117 91177308-0d34-0410-b5e6-96231b3b80d8
Resurrect r191017 " GVN proceeds in the presence of dead code" plus a fix to PR17307 & 17308.

  The problem of r191017 is that when GVN fabricate a val-number for a dead instruction (in order
to make following expr-PRE happy), it forget to fabricate a leader-table entry for it as well.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191118 91177308-0d34-0410-b5e6-96231b3b80d8
Move emission of the debug string table to early in the debug
info finalization to greatly reduce the number of fixups that the
assembler has to handle in order to improve compile time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191119 91177308-0d34-0410-b5e6-96231b3b80d8