Auto merge of #1404 - auscompgeek:fix-args-are-cpp, r=emilio
Auto merge of #1404 - auscompgeek:fix-args-are-cpp, r=emilio

Fix args_are_cpp to look for -x without =

Clang doesn't allow `=` between `-x` and the language name.

rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen