Update bindgen build dependency to 0.50

As of 0.49, bindgen supports a BINDGEN_EXTRA_CLANG_ARGS environment variable
that can be used to pass extra arguments to clang. This can be used
instead of COREAUDIO_CFLAGS.

Cargo.toml

@@ -11,7 +11,7 @@ repository = "https://github.com/RustAudio/coreaudio-sys.git"
 build = "build.rs"
 
 [build-dependencies]
-bindgen = "0.42"
+bindgen = "0.50"
 
 [features]
 default = ["audio_toolbox", "audio_unit", "core_audio", "open_al", "core_midi"]

build.rs

@@ -74,6 +74,7 @@ fn build(sdk_path: &str, target: &str) {
         }
     }
 
+    println!("cargo:rerun-if-env-changed=BINDGEN_EXTRA_CLANG_ARGS");
     // Get the cargo out directory.
     let out_dir = PathBuf::from(env::var("OUT_DIR").expect("env variable OUT_DIR not found"));
 
@@ -94,11 +95,6 @@ fn build(sdk_path: &str, target: &str) {
         .derive_default(true)
         .rustfmt_bindings(false);
 
-    println!("cargo:rerun-if-env-changed=COREAUDIO_CFLAGS");
-    if let Ok(cflags) = std::env::var("COREAUDIO_CFLAGS") {
-        builder = builder.clang_args(cflags.split(" "));
-    }
-
     let bindings = builder.generate().expect("unable to generate bindings");
 
     // Write them to the crate root.