Implement template instantiation for the prefix unary operators. As

Implement template instantiation for the prefix unary operators. As
always, refactored the existing logic to tease apart the parser action
and the semantic analysis shared by the parser and template
instantiation.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@66987 91177308-0d34-0410-b5e6-96231b3b80d8