The implementation of `fesetenv` cannot be portable, as the value of
`FE_DFL_ENV` differs between platforms. On FreeBSD, it is a actual
environment. With glibc however, it's a sentinel -1 handled in the
implementation of its floating point functions.
With openlibm based on FreeBSD's libm, it assumes `FE_DFL_ENV` to be an
actual environment. That assumption breaks using code that was compiled
against glibc, e.g., `libcuda`:
```
Thread 1 "julia-debug" received signal SIGSEGV, Segmentation fault.
0x00007ffff7b855d0 in fesetenv () from /home/tim/Julia/julia/build/release/usr/bin/../lib/libopenlibm.so
(gdb) bt
```
This reverts commit 5a27b4c0c0a5befc2b7622ff8517743963c1f1d2.
Fixes https://github.com/JuliaLang/julia/issues/38427.
be31bff11d