[analyzer] Refactoring: Move checkers into lib/GR/Checkers and their own library, libclangGRCheckers

llvm-svn: 122422

llvm-svn: 122421

llvm-svn: 122420

llvm-svn: 122270

llvm-svn: 99731

to various MacOS X functions.  The checks in BasicObjCFoundationChecks.cpp will
gradually be migrated here.

As a first check, check that when 'dispatch_once()' is passed a predicate value
that has non-local storage.

llvm-svn: 97116