Removed option "-parse-ast-check" from clang driver. This is now implemented

using "-parse-ast -verify".

Updated all test cases (using a sed script) that invoked -parse-ast-check to
now use -parse-ast -verify.

Fixed a bug where using "-verify" instead of "-parse-ast-check" would not
correctly create the DiagClient needed to accumulate diagnostics.

llvm-svn: 42365