Can't build stdlib for mips-unknown-linux-musl without libunwind

[skade]

I'm trying rebuild stdlib for the OpenWRT malta SDK (available here: https://downloads.openwrt.org/releases/18.06.2/targets/malta/be/openwrt-sdk-18.06.2-malta-be_gcc-7.3.0_musl.Linux-x86_64.tar.xz).

The SDK ships with libgcc_s.so, but without libunwind.a, leading to a linker error when building unwind. I'd like to run with panic=abort, so I don't need unwinding.

error: could not find native static library unwind, perhaps an -L flag is missing?

mips is special-cased in libunwind here: https://github.com/rust-lang/rust/blob/master/src/libunwind/lib.rs#L28-L31

I tried passing target-feature=-crt-static and using a custom target target:

  "crt-static-default": false,
  "crt-static-respected": true,
  "dynamic-linking": true,

Both don't work.

Steps to reproduce:

• Unzip the SDK
• Make sure openwrt-sdk-18.06.2-malta-be_gcc-7.3.0_musl.Linux-x86_64/staging_dir/toolchain-mips_24kc_gcc-7.3.0_musl/bin/ is in PATH
• Set the linker:

[target.mips-openwrt-linux-musl]
linker = "mips-openwrt-linux-gcc"

• Use Xargo to rebuild stdlib

Building and running a binary works when modifying the code above to just link gcc_s:

#[cfg(target_env = "musl")]
#[link(name = "gcc_s")]
extern {}