Since "half" is an OpenCL keyword and clang accepts __fp16 as an extension for
other languages, error messages and metadata (and hence debug info) should refer
to the half-precision floating point as "__fp16" instead of "half" when
compiling for non-OpenCL languages. This patch creates a new printing policy for
half in a similar manner to what is done for bool and wchar_t.

Differential Revision: http://llvm-reviews.chandlerc.com/D2952



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204164 91177308-0d34-0410-b5e6-96231b3b80d8