[OPENMP]Initial support for the delayed diagnostics.

It is important to delay the emission of the diagnostic messages for the
functions unless it is proved that the function is going to be used on
the device side. It is required to support compilation with some of the
target-specific system headers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@353540 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed