Add ArrayRef<> interface to get the formal parameters of a BlockDecl.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199471 91177308-0d34-0410-b5e6-96231b3b80d8
Change CallEvent to use ArrayRef<> interface to get formal parameters of callee.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199472 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Teach NonNullParamChecker about 'nonnull' attributes on parameters.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199473 91177308-0d34-0410-b5e6-96231b3b80d8