[libc-commits] [libc] [libc][math][c23] Add acospif16() function (PR #132754)

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lntue wrote:

> @amemov Are you still working on this? The CI build failed due to this error:
> 
> ```
> /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-clshd-1/llvm-project/github-pull-requests/libc/utils/MPFRWrapper/MPCommon.cpp:75:3: error: use of undeclared identifier 'mpfr_acospi'
> ```
> 
> I assume this is once again due to the CI using an older version of MPFR. @lntue

We need to add a workaround for older versions of MPFR then.  At least it is quite straightforward for `acospi`.

https://github.com/llvm/llvm-project/pull/132754