Link against clang runtime on static builds on macOS

On OSX we need to link against the clang runtime, which is hidden in some non-default path.
We can get the path from `clang --print-search-dirs`.
Kudos to @ehuss for finding that workaround.

Fixes #279.

Author: badboy

curl-sys/build.rs

@@ -47,6 +47,13 @@ fn main() {
             .status();
     }
 
+    if target.contains("apple") {
+        // On OSX we need to link against the clang runtime, which is hidden in some non-default
+        // path.
+        println!("cargo:rustc-link-lib=clang_rt.osx");
+        println!("cargo:rustc-link-search={}", macos_link_search_path());
+    }
+
     let dst = PathBuf::from(env::var_os("OUT_DIR").unwrap());
     let include = dst.join("include");
     let build = dst.join("build");
@@ -467,3 +474,23 @@ fn curl_config_reports_http2() -> bool {
 
     return true;
 }
+
+fn macos_link_search_path() -> String {
+    let output = Command::new("clang").arg("--print-search-dirs").output().unwrap();
+    if !output.status.success() {
+        panic!("Can't get search paths from clang");
+    }
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    if !stdout.contains("libraries: ") {
+    }
+
+    for line in stdout.lines() {
+        if line.contains("libraries: =") {
+            let path = line.split('=').skip(1).next().unwrap();
+            return format!("{}/lib/darwin", path);
+        }
+    }
+
+    panic!("clang is missing search paths");
+}