Add another keyword-selection flag to CorrectionCandidateCallback.

The new flag, WantFunctionLikeCasts, covers a subset of the keywords
covered by WantTypeSpecifiers that can be used in casts that look like
function calls, e.g. "return long(5);", while excluding the keywords
like "enum" and "const" that would be included when WantTypeSpecifiers
is true but cannot be used in something that looks like a function call.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@214109 91177308-0d34-0410-b5e6-96231b3b80d8