Update test_utils to use cc rather than gcc.

The `gcc` crate has been replaced with `cc`. Additionally, the
`gcc:Config` was renamed to `gcc::Build`. This updates both of
those.

Commit taken from SSheldon/rust-block#8

Author: waywardmonkeys

objc_test_utils/Cargo.toml

@@ -17,4 +17,4 @@ license = "MIT"
 build = "build.rs"
 
 [build-dependencies]
-gcc = "0.3"
+cc = "1.0"

objc_test_utils/build.rs

@@ -1,7 +1,7 @@
-extern crate gcc;
+extern crate cc;
 
 fn main() {
-    gcc::Config::new()
+    cc::Build::new()
         .compiler("clang")
         .file("extern/block_utils.c")
         .flag("-fblocks")