servo: Merge #6306 - Use Cargo's target directory sharing (from metajack:shared-target-dir); r=mbrubeck

This speeds up `./mach build --dev` followed by `./mach build-cef` by
25%. When rust-lang/cargo#497 is fixed, this speedup will increase
dramatically.

Source-Repo: https://github.com/servo/servo
Source-Revision: d6263c9b6e969fde4c644034e684a39d68667ad9

servo/python/tidy.py

@@ -36,8 +36,7 @@ ignored_files = [
     # Generated and upstream code combined with our own. Could use cleanup
     "components/script/dom/bindings/codegen/*",
     "components/style/properties/mod.rs",
-    "components/servo/target/*",
-    "ports/gonk/target/*",
+    "target/*",
     "ports/gonk/src/native_window_glue.cpp",
     "ports/cef/*",