[clang] [llvm] [X86] Reduce -ffixed-r compile-time overhead (PR #184606)

[Alexis Engelke via cfe-commits]

aengelke wrote:

Seems to fix the regression: https://llvm-compile-time-tracker.com/compare.php?from=9c2829f2e1883a8634edf4008f1cbc5928c63eeb&to=b04125bf42a82fb7b852fbc74d08a9be749bfde4&stat=instructions:u

https://github.com/llvm/llvm-project/pull/184606