[clang] [libc] [llvm] [clang] Make __builtin_exp and __builtin_expf constexpr. (PR #199808)

[via cfe-commits]

lntue wrote:

The current failing CIs are unrelated:

```
2026-07-17T13:32:01.8655537Z ********************
2026-07-17T13:32:01.8655758Z Failed Tests (2):
2026-07-17T13:32:01.8656008Z   Profile-x86_64 :: Linux/counter_promo_for.c
2026-07-17T13:32:01.8656377Z   Profile-x86_64 :: Linux/counter_promo_while.c
2026-07-17T13:32:01.8656586Z 
2026-07-17T13:32:01.8656591Z 
2026-07-17T13:32:01.8656688Z Testing Time: 57.98s
2026-07-17T13:32:01.8656820Z 
2026-07-17T13:32:01.8656932Z Total Discovered Tests: 8543
2026-07-17T13:32:01.8657188Z   Skipped          :   38 (0.44%)
2026-07-17T13:32:01.8657453Z   Unsupported      : 1280 (14.98%)
2026-07-17T13:32:01.8657708Z   Passed           : 7141 (83.59%)
2026-07-17T13:32:01.8657961Z   Expectedly Failed:   82 (0.96%)
2026-07-17T13:32:01.8658208Z   Failed           :    2 (0.02%)
2026-07-17T13:32:01.8955160Z FAILED: compiler-rt/test/CMakeFiles/check-compiler-rt /home/gha/actions-runner/_work/llvm-project/llvm-project/build/runtimes/runtimes-bins/compiler-rt/test/CMakeFiles/check-compiler-rt 
```


https://github.com/llvm/llvm-project/pull/199808