Debug info: Support variadic functions.
Variadic functions have an unspecified parameter tag after the last
argument. In IR this is represented as an unspecified parameter in the
subroutine type.

Paired commit with CFE.

rdar://problem/13690847

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202184 91177308-0d34-0410-b5e6-96231b3b80d8
Remove outdated comments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202186 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "Debug info: Support variadic functions."

This reverts commit r202184 because of buildbot breakage.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202187 91177308-0d34-0410-b5e6-96231b3b80d8