[clang] [clang] Allow custom bug report messages (PR #157536)

[Alan Zhao via cfe-commits]

alanzhao1 wrote:

> Note that there are a couple of clang regression tests that check for the "PLEASE submit a bug report" text; any patch here also needs to update those tests.

Unless I'm missing something this patch as is should be fine - it only changes the text if the macro is set.

https://github.com/llvm/llvm-project/pull/157536