[clang] [Clang] Don't give up on an unsuccessful function instantiation (PR #126723)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

> > Technically swapping the first and second branches I mentioned above should work, but the last time I tried that it caused a regression and was reverted."
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> 
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> Yeah, swapping the branches would have been a much simpler fix.
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> What was the regression? Do we have test case for it anywhere?

https://github.com/llvm/llvm-project/pull/98991


https://github.com/llvm/llvm-project/pull/126723