[CUDA][HIP][OpenMP] Emit deferred diagnostics by a post-parsing AST travese

This patch removes the explicit call graph for CUDA/HIP/OpenMP deferred
diagnostics generated during parsing since it is error prone due to
incomplete information about function declarations during parsing. In stead,
this patch does a post-parsing AST traverse and emits deferred diagnostics
based on the use graph implicitly generated during the traverse.

Differential Revision: https://reviews.llvm.org/D70172