[mips] Add NaCl target and forbid indexed loads and stores for it

This patch adds NaCl target for Mips. It also forbids indexed loads and
stores if the target is NaCl.

Patch by Sasa Stankovic.

Differential Revision: http://llvm-reviews.chandlerc.com/D2690
MS ABI: Mangle member pointer template arguments

Member pointers are mangled as they would be represented at runtime.
They can be a single integer literal, single decl, or a tuple with some
more numbers tossed in.  With Clang today, most of those numbers will be
zero because we reject pointers to members of virtual bases.

This change required moving VTableContextBase ownership from
CodeGenVTables to ASTContext, because mangling now depends on vtable
layout.

I also hoisted the inheritance model helpers up to be inline static
methods of MSInheritanceAttr.  This makes the AST code that deals with
member pointers much more readable.

MSVC doesn't appear to have stable manglings of null member pointers:
- Null data memptrs in function templates have a mangling collision with
  the first field of a non-polymorphic single inheritance class.
- The mangling of null data memptrs changes if you add casts.
- Large null function memptrs in class templates crash MSVC.

Clang uses the class template mangling for null data memptrs and the
function template mangling for null function memptrs to deal with this.

Reviewers: majnemer

Differential Revision: http://llvm-reviews.chandlerc.com/D2695
Revert "Fix an invalid check for duplicate option categories."

This reverts commit r200853.

It was causing clang/Analysis/checker-plugins.c to crash.
Fixed indentation.
Fixed an issue where "command source" would not do the right thing:
- empty lines in init files would repeat previous command and cause errors to be displayed
- all options to control showing the command, its output, if it should stop on error or continue, weren't being obeyed.
Remove unused variable to fix -Werror build
Remove support for not using .loc directives.

Clang itself was not using this. The only way to access it was via llc.
Update for llvm api change.