Remove implicit conversion that promotes half to other larger precision types...

Remove implicit conversion that promotes half to other larger precision types for fp classification builtins

Summary:
It shouldn't promote half to double or any larger precision types for fp classification builtins.
Because fp classification builtins would get incorrect result with promoted argument.
For example, __builtin_isnormal with a subnormal half value should return false, but it is not.
That the subnormal half value is promoted to a normal double value.

Reviewers: aaron.ballman

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D71049