SIGILL on arm-unknown-linux-musleabi binaries with lto

[adrian-budau]

On target arm-unknown-linux-musleabi (and arm-unknown-linux-musleabihf) any binary compiled with lto will fail with SIGILL on latest stable (1.29.0 as of this time).

After some searching it seems the culprit is #52087 which was meant to fix aarch64-unknown-linux-musl until musl 1.1.20 was out. Unfortunately the patch for musl used in that pull request broke arm-unknown-linux-musleabi. This was later fixed in https://git.musl-libc.org/cgit/musl/commit/?id=c06c1eb6610b478a06df8116aefc975f376760f8 which also landed in musl 1.1.20.