[llvm] Enable exp10 libcall on linux (PR #68736)

[Nikita Popov via llvm-commits]

nikic wrote:

I went ahead and reverted this change. I could have fixed the uncovered switch warning, but the change in general looks problematic to me.

The comment indicates that these functions are broken prior to glibc 2.18 -- however, a common glibc baseline for binary distribution is glibc 2.17, because it is used by CentOS/RHEL 7. This is the glibc baseline that Rust uses, for example. If you want to increase the glibc requirements of LLVM-generated binaries, then that needs a wider discussion than this pull request (or more research to show that this is safe, e.g. because distros using glibc 2.17 have backported the necessary fixes or so).

There are also some buildbots failing with `undefined symbol: __exp10` after this change, for example https://lab.llvm.org/buildbot/#/builders/239/builds/6232.

https://github.com/llvm/llvm-project/pull/68736