New comment by ericonr on void-packages repository

https://github.com/void-linux/void-packages/pull/28396#issuecomment-771174763

Comment:
About cross, when trying a build for armv7l-musl:

```
  TARGET = Some("x86_64-unknown-linux-musl")
  HOST = Some("x86_64-unknown-linux-musl")
  CC_x86_64-unknown-linux-musl = None
  CC_x86_64_unknown_linux_musl = None
  HOST_CC = None
  CC = Some("armv7l-linux-musleabihf-gcc")
  CFLAGS_x86_64-unknown-linux-musl = None
  CFLAGS_x86_64_unknown_linux_musl = None
  HOST_CFLAGS = None
  CFLAGS = Some("-fstack-clash-protection -D_FORTIFY_SOURCE=2 -O2 -pipe -march=armv7-a -mfpu=vfpv3 -mfloat-abi=hard   -I/usr/armv7l-linux-musleabihf/usr/include")
  CRATE_CC_NO_DEFAULTS = None
  DEBUG = Some("true")
  CARGO_CFG_TARGET_FEATURE = Some("fxsr,sse,sse2")
  running: "armv7l-linux-musleabihf-gcc" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "-m64" "-fstack-clash-protection" "-D_FORTIFY_SOURCE=2" "-O2" "-pipe" "-march=armv7-a" "-mfpu=vfpv3" "-mfloat-abi=hard" "-I/usr/armv7l-linux-musleabihf/usr/include" "-I" "/usr/armv7l-linux-musleabihf/usr/include" "-E" "build/expando.c"
```

What this means: maturin isn't passing target to cargo correctly; since `TARGET` is incorrect, together with `CARGO_CFG_TARGET_FEATURE`. Also, `cargo` unconditionally adds `"-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "-m64"` to the compiler command line.

Fruthermore, `openssl-sys` gets into the build via addr -> psl -> psl-codegen -> psl-lexer -> native-tls -> openssl. I have no idea if it's truly necessary, but if anything those are the scripts to investigate.

I'm not sure it's really maturin's fault, since it shows an appropriate cargo command line.