This commit fixes several things.
1) It enables usage of vendor crates, making our patches actually
do something (those for the vendor/ subdirectory anyway)
2) By extension, it enables dynamic linking of musl, which was not
being done at all.
3) Removes the ugly LDFLAGS hack, which was causing miscompilation
in cross environments, as it didn't pass the cross sysroot to
search for libs in when linking. This resulted in a particularly
bad miscompilation when cross-compiling from glibc to musl on
the same architecture, as it would link against glibc's libc.a
instead of musl's libc.a (not libc.so because the musl dynamic
link patch was not being used), resulting in failures when
actually compiling various projects. This hack is now replaced
with properly patching the lzma-sys crate instead, which was
the culprit previously when it comes to failures.
[ci skip]
a57bfd40e8