extern crate cc;

fn main() {

    let asm_path = if cfg!(target_os = "macos") {
        "src/generic.c"
    } else if cfg!(target_arch = "x86") {
        "src/x86.S"
    } else if cfg!(target_arch = "x86_64") {
        "src/x64.S"
    } else {
        "src/generic.c"
    };
    cc::Build::new()
        .file(asm_path)
        .opt_level(3)
        .compile("sha1-round");
}

extern crate cc;

fn main() {
    let asm_path = if cfg!(target_arch = "x86") {
        "src/x86.S"
    } else if cfg!(target_arch = "x86_64") {
        "src/x64.S"
    } else {
        "src/generic.c"
    };
    cc::Build::new()
        .file(asm_path)
        .opt_level(3)
        .compile("sha1-round");
}

--- 
+++ 
@@ -1,7 +1,10 @@
 extern crate cc;
 
 fn main() {
-    let asm_path = if cfg!(target_arch = "x86") {
+
+    let asm_path = if cfg!(target_os = "macos") {
+        "src/generic.c"
+    } else if cfg!(target_arch = "x86") {
         "src/x86.S"
     } else if cfg!(target_arch = "x86_64") {
         "src/x64.S"
Disable asm sha1 rounds on OSX
