[compiler-rt] [compiler-rt][builtins] Enable i386 long double to float128 conversions (PR #201078)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson approved this pull request.

Thanks, LGTM. Will merge once I've got around to testing this locally since I'm not sure if CI tests this. 

https://github.com/llvm/llvm-project/pull/201078