build failed even with with suggested rustc alias

I'm getting a build error when trying to run a musl build. It may just be bad error reporting on cargo's part but the error reported is

```
failed to execute command: No such file or directory (os error 2)
Is `musl-gcc` not installed?
```

It looks like some crates were successful but the error seems to happen on the openssl crate.

The full error is below.

```
Build failed, waiting for other jobs to finish...
failed to run custom build command for `openssl v0.7.6`
Process didn't exit successfully: `/source/target/release/build/openssl-09576f2f9776fa80/build-script-build` (exit code: 101)
--- stdout
TARGET = Some("x86_64-unknown-linux-musl")
OPT_LEVEL = Some("3")
PROFILE = Some("release")
TARGET = Some("x86_64-unknown-linux-musl")
debug=false opt-level=3
HOST = Some("x86_64-unknown-linux-gnu")
TARGET = Some("x86_64-unknown-linux-musl")
TARGET = Some("x86_64-unknown-linux-musl")
HOST = Some("x86_64-unknown-linux-gnu")
CC_x86_64-unknown-linux-musl = None
CC_x86_64_unknown_linux_musl = None
TARGET_CC = None
CC = None
HOST = Some("x86_64-unknown-linux-gnu")
TARGET = Some("x86_64-unknown-linux-musl")
HOST = Some("x86_64-unknown-linux-gnu")
CFLAGS_x86_64-unknown-linux-musl = None
CFLAGS_x86_64_unknown_linux_musl = None
TARGET_CFLAGS = None
CFLAGS = None
running: "musl-gcc" "-O3" "-ffunction-sections" "-fdata-sections" "-m64" "-fPIC" "-static" "-o" "/source/target/x86_64-unknown-linux-musl/release/build/openssl-09576f2f9776fa80/out/src/c_helpers.o" "-c" "src/c_helpers.c"

failed to execute command: No such file or directory (os error 2)
Is `musl-gcc` not installed?

--- stderr
thread '' panicked at 'explicit panic', /root/.cargo/registry/src/github.com-88ac128001ac3a9a/gcc-0.3.24/src/lib.rs:809
```