Fix building for musl libc

src/compile.rs

@@ -5,6 +5,7 @@ use anyhow::{anyhow, bail, Context, Result};
 use fat_macho::FatWriter;
 use fs_err::{self as fs, File};
 use std::collections::HashMap;
+use std::env;
 use std::io::{BufReader, Read};
 use std::path::PathBuf;
 use std::process::{Command, Stdio};
@@ -162,9 +163,14 @@ fn compile_target(
         .iter()
         .fold("cargo".to_string(), |acc, x| acc + " " + x);
 
+    let mut rust_flags = env::var_os("RUSTFLAGS").unwrap_or_default();
+    if context.target.is_musl_target() {
+        rust_flags.push(" -C target-feature=-crt-static");
+    }
     let mut let_binding = Command::new("cargo");
     let build_command = let_binding
         .args(&build_args)
+        .env("RUSTFLAGS", rust_flags)
         // We need to capture the json messages
         .stdout(Stdio::piped())
         // We can't get colored human and json messages from rustc as they are mutually exclusive,

src/target.rs

@@ -1,5 +1,6 @@
 use anyhow::{bail, format_err, Result};
 use platform_info::*;
+use platforms::target::Env;
 use platforms::Platform;
 use serde::{Deserialize, Serialize};
 use std::env;
@@ -80,6 +81,7 @@ impl fmt::Display for Arch {
 pub struct Target {
     os: OS,
     arch: Arch,
+    env: Option<Env>,
 }
 
 impl Target {
@@ -139,7 +141,11 @@ impl Target {
             (OS::Windows, Arch::ARMV7L) => bail!("armv7l is not supported for Windows"),
             (_, _) => {}
         }
-        Ok(Target { os, arch })
+        Ok(Target {
+            os,
+            arch,
+            env: platform.target_env,
+        })
     }
 
     /// Returns whether the platform is 64 bit or 32 bit
@@ -179,6 +185,15 @@ impl Target {
         self.os == OS::Windows
     }
 
+    /// Returns true if the current platform's target env is Musl
+    pub fn is_musl_target(&self) -> bool {
+        match self.env {
+            Some(Env::Musl) => true,
+            Some(_) => false,
+            None => false,
+        }
+    }
+
     /// Returns the platform part of the tag for the wheel name for cffi wheels
     pub fn get_platform_tag(&self, manylinux: &Manylinux, universal2: bool) -> String {
         match (&self.os, &self.arch) {