[clang] [Clang] fix crash in codegen caused by deferred asm diagnostics under -fopenmp (PR #147163)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

There's one other possibility... you could make "deferred" diagnostics not defer diagnosing quite so much.  If the function is defined in a way that it inherently must be emitted, or it's already been odr-used, there's no point to actually deferring the diagnostic: we know we'll emit it eventually.  Otherwise, we wait until we see an ODR-use of the function: if we see such a use, we immediately diagnose that use.  But I'm not quite sure how you deal with a function that's declared early, then defined inline later in the file; you'd need to recursively scan all the callers of the function.

Sticking a map in the ASTContext is probably okay.

https://github.com/llvm/llvm-project/pull/147163