MS ABI: Emit an error during IRgen on C++ exception handling

Currently, users get error messages about RTTI descriptor mangling with
no useful source location.  This addresses that.

Another approach would be to disable C++ exceptions by default in the
driver when using the Microsoft C++ ABI.  However, this makes it
impossible to parse system headers that use exception handling
constructs.  By delaying the error to IRgen, we can figure out if we
actually need to emit code for this construct.  Additionally, users who
are only interested in building refactoring tools on Windows still get a
correct AST without having to add flags.  Finally, this is consistent
with what we do for SEH.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207999 91177308-0d34-0410-b5e6-96231b3b80d8
Simplify replacement map by avoiding duplicate values and ensuring the values it does contain are necessary.

Items were being redundantly added to the replacement map (both when the
declaration was created, and then again when its definition was
constructed) which caused extra handling to be required when walking the
map (as elements may've already been replaced due to prior entries). By
avoiding adding the duplicates, the checks in the replacement handling
can be replaced with assertions.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208000 91177308-0d34-0410-b5e6-96231b3b80d8
Add -Wnon-modular-include* options

Warn on non-modular includes in various contexts.

-Wnon-modular-include
 -Wnon-modular-include-in-module
  -Wnon-modular-include-in-framework-module

Where each group is a subgroup of those above it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208004 91177308-0d34-0410-b5e6-96231b3b80d8