Submitted by:
Reviewed by:
- Finished semantic analysis for vectors, added some diagnostics.
- Added AST for vectors (instantiation, installation into the decl).
- Fixed bug in ParseArraySubscriptExpr()...this crasher was introduced by me
when we added the range support.
- Turned pedantic off by default. Since vectors are gcc extensions, having
pedantic on by default was annoying. Turning it off by default is  also
consistent with gcc (but this wasn't my primary motivation).
- Tweaked some comments and diagnostics.

Note: The type checking code is still under construction (for vectors). This
will be my next check-in.

llvm-svn: 39715