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

[Younan Zhang via cfe-commits]

zyn0217 wrote:

Compile time tracker: http://llvm-compile-time-tracker.com/compare.php?from=83a8bb363ad578da67a7cb568460a3871ce0ad8b&to=21ca76a13ca62715ce98fb2c8b0361df727769b0

I think the difference is acceptable?

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