Alpine Linux has a variety of patches to allow GHC to build against the musl libc implementation. Let's get these upstream.

Here is my take on the patches:

• 0000-alpine.patch: This is a no-brainer. Merged as 9ae24bb6.
• 0000-bootstrap.patch: I really don't know about this one. The motivation is quite unclear. Needs discussion.
• 0001-rm-ghc-pwd.patch: Already merged in 4c56ad36.
• 0002-Correct-issue-with-libffi-and-glibc.patch: This is, unfortunately, a libffi fix, not a GHC fix. I'm not enthusiastic about patching libffi like this. However, libffi's upstream is quite unresponsive and we are waiting for them to act on a number of issues, so perhaps we'll need to reconsider this. I've created #14056 (closed) to track this.
• 0003-do-not-use-SHELL.patch: Looks reasonable to me. Merged as a10c2e6e.
• 0004-reproducible-tmp-names.patch: Seems plausible.
• 0005-buildpath-abi-stability.patch: There's some discussion in #10424.
• 0006-fix-madvise.patch: Merged in 6576bf83. See #12865 (closed)
• 0007-build-hp2ps-twice.patch, 0008-build-unlit-twice.patch: Why?