build: remove openlibm

[inkydragon]

See if we've got some progress for #42299

After using gcc14 and updating the CSL,
I was able to build successfully locally and pass most of the stable tests.
Let's see if we can build successfully on the mainline and pass the tests.

[inkydragon]

I had a crazy idea: since libc on windows (msvcrt) is missing some functions, let's wrap and use those functions from C++ (libstdc++).

[inkydragon]

do not merge this pr.

[inkydragon]

With newer msvcrt from gcc14, we can build julia-x64 without openblibm
https://buildkite.com/julialang/julia-master/builds/43184#0193e4ca-544e-43fd-b419-b3c2d245ba39

[inkydragon]

Now, we passed all tests on x86 and x64

https://buildkite.com/julialang/julia-master/builds/43191#0193e8a8-9d95-47cb-95e9-403619dd44ed

[giordano]

With newer msvcrt from gcc14, we can build julia-x64 without openblibm

Does this mean that on Windows we'd need to require a very recent compiler?

[inkydragon]

Does this mean that on Windows we'd need to require a very recent compiler?

MSYS2 only keeps the latest version of the package, so GCC 14 is used here.

Maybe a newer version of gcc isn't necessary, but I haven't tested it yet.
I guess just using the mingw toolchain and linking to mingw32, mingwex, msvcrt would be an alternative to openlibm.