[clang][PCH] Don't try to create standalone debug-info for types marked nodebug (#123253)

Fixes one of the crashes uncovered by
https://github.com/llvm/llvm-project/pull/118710

`getOrCreateStand

[clang][PCH] Don't try to create standalone debug-info for types marked nodebug (#123253)

Fixes one of the crashes uncovered by
https://github.com/llvm/llvm-project/pull/118710

`getOrCreateStandaloneType` asserts that a `DIType` was created for the
requested type. If the `Decl` was marked `nodebug`, however, we can't
generate debug-info for it, so we would previously trigger the assert.
For now keep the assertion around and check the `nodebug` at the
callsite.

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