Set --target flag for Apple's clang when cross-compiling

Author: kornelski

build.rs

@@ -209,6 +209,14 @@ fn build(target_os: &str) -> io::Result<()> {
         // The cc crate has the messy logic of guessing a working prefix,
         // and this is a messy way of reusing that logic.
         let cc = cc::Build::new();
+
+        // Apple-clang needs this, -arch is not enough.
+        let target_flag = format!("--target={}", target);
+        if cc.is_flag_supported(&target_flag).unwrap_or(false) {
+            configure.arg(format!("--extra-cflags={}", target_flag));
+            configure.arg(format!("--extra-ldflags={}", target_flag));
+        }
+
         let compiler = cc.get_compiler();
         let compiler = compiler.path().file_stem().unwrap().to_str().unwrap();
         if let Some(suffix_pos) = compiler.rfind('-') {
@@ -340,6 +348,8 @@ fn build(target_os: &str) -> io::Result<()> {
     // configure misc build options
     enable!(configure, "BUILD_PIC", "pic");
 
+    println!("configure cmd: {:?}", configure);
+
     // run ./configure
     let output = configure
         .output()