Dynamically load libm on Linux for each new session

[lukel97]

This fixes the issue on Linux where the binary was statically linked and Template Haskell (or the eval plugin on haskell-language-server) tried to evaluate some code. It would previously fail to load ghc-prim because it couldn't lookup symbols from libm which are usually dynamically linked in.

See haskell/haskell-language-server#221

Unfortunately we can't just statically link in libm and have the binary dlsym on itself apparently: https://stackoverflow.com/questions/14289488/use-dlsym-on-a-static-binary

So now the statically linked binary actually dynamically links in libm on a "best-effort" case: From what I can tell if libm is not available this will just print an error to stderr and carry on as usual (albeit it will trip up on Template Haskell), and if the binary dynamically linked then this will have no effect.

cc @pepeiborra

[pepeiborra]

I don't know if this is the best solution, but in any case it buys some time until we can figure it out. Thanks for the continued digging on this @bubba !

[pepeiborra]

A fair point to make is that currently this is only relevant for HLS, and therefore maybe it belongs in the HLS Main module

[lukel97]

There was a way I saw originally to load in libm without the HscEnv which we could do, I'm not 100% sure what the difference is though. At some point we should also revisit this and see what is the correct way to fix this in the long term

[pepeiborra]

Can you rebase or otherwise retrigger CI somehow? I need a green light to merge!

[cocreature]

@pepeiborra /azp run should work for anyone with write access to the repo I believe.

[lukel97]

/azp run

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No pipelines are associated with this pull request.

[cocreature]

hm /azp run probably got lost in the repo transfer. Try it out on new PRs.