Revert "Merge pull request rust-lang#1489 from KyleMayes/clang-sys"

This reverts commit 0d004a7, reversing
changes made to 2a01e8d.

Author: emilio

Cargo.lock

@@ -48,7 +48,7 @@ cexpr = "0.3.3"
 cfg-if = "0.1.0"
 # This kinda sucks: https://github.com/rust-lang/cargo/issues/1982
 clap = "2"
-clang-sys = { version = "0.27.0", features = ["runtime", "clang_6_0"] }
+clang-sys = { version = "0.26.4", features = ["runtime", "clang_6_0"] }
 lazy_static = "1"
 peeking_take_while = "0.1.2"
 quote = { version = "0.6", default-features = false }