[libc-commits] [libc] [libc] Use `${libc_opt_high_flag}` instead of `-O3` (PR #123233)

[Petr Hosek via libc-commits]

petrhosek wrote:

> Can you take a look at the Windows presubmit failure?

Looks like the optimization flag is being passed to both the compiler and the linker. That's fine on Linux or macOS since `clang` is invoked as the linker and it'll consume the optimization flag, but on Windows we invoke the linker directly and `lld-link` (or `link`) doesn't handle `/O2`. I don't know why this works now, it's possible that `lld-link` just consumes and ignores `-O3`.

https://github.com/llvm/llvm-project/pull/123233