Updated build.rs to tell RustC that dxgi, quartz and x11 are expected configurations.

Added lifetime annotations to various methods in common/aom.rs and common/vpxcodec.rs.
Updated common/vpx.rs to allow unused_imports in the generated bindings.
Updated dxgi/mag.rs to allow non_snake_case identifiers like "dwFilterMode".

libs/scrap/build.rs

@@ -227,6 +227,9 @@ fn ffmpeg() {
 */
 
 fn main() {
+    // in this crate, these are also valid configurations
+    println!("cargo::rustc-check-cfg=cfg(dxgi,quartz,x11)");
+
     // there is problem with cfg(target_os) in build.rs, so use our workaround
     let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap();