Handle constructors and destructors a bit more uniformly in CodeGen.

There were code paths that are duplicated for constructors and destructors just
because we have both CXXCtorType and CXXDtorsTypes.

This patch introduces an unified enum and reduces code deplication a bit.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@217383 91177308-0d34-0410-b5e6-96231b3b80d8
Add a comment for something that confused me.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@217384 91177308-0d34-0410-b5e6-96231b3b80d8
Make FileEntry::getName() valid across calls to FileManager::getFile()

Because we may change the name of a FileEntry inside getFile, the name
returned by FileEntry::getName() could be destroyed.  This was causing a
use-after-free when searching the HeaderFileInfo on-disk hashtable for a
module or pch.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@217385 91177308-0d34-0410-b5e6-96231b3b80d8
Remove a parameter that has been unused since r188481. No behavior change.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@217386 91177308-0d34-0410-b5e6-96231b3b80d8