Reland [clang] Check unsupported types in expressions

This was committed as ec6c8471, but then reverted after a failure
in: https://lab.llvm.org/buildbot/#/builders/84/builds/13983

I was not able to reproduce the problem, but I added an extra check
for a NULL QualType just in case.

Original comit message:

The patch adds missing diagnostics for cases like:

  float F3 = ((__float128)F1 * (__float128)F2) / 2.0f;

Sema::checkDeviceDecl (renamed to checkTypeSupport) is changed to work
with a type without the corresponding ValueDecl. It is also refactored
so that host diagnostics for unsupported types can be added here as
well.

Differential Revision: https://reviews.llvm.org/D109315