stack unofficial fully statically linked with musl

I've made a fully statically linked version of stack by linking it against musl instead of glibc, using nix's musl cross-compilation toolchain:

• For Linux x86_64: stack-1.6.5-unofficial-fully-static-musl
• For Linux x86_64: stack-1.7.1-unofficial-fully-static-musl

Build files are here.

Update: The Stack 1.9 official release is using this approach.