Use Cargo's target directory sharing.

This speeds up `./mach build --dev` followed by `./mach build-cef` by a
large amount, and also speeds up other build combos found in our CI.

tests/power/PowerMeasure.py

@@ -44,7 +44,7 @@ def PowerCollector(OutputDir, Benchmarks, LayoutThreads, Renderer):
                 power_dir, "power-Layout%d-set%d.csv" % (layoutT, ExpNum))
             TimeFiles = path.join(
                 time_dir, "time-Layout%d-set%d.csv" % (layoutT, ExpNum))
-            ServoCmd = "(time ../../components/servo/target/release/servo -x -y %d %s %s) 2> %s" % \
+            ServoCmd = "(time ../../target/release/servo -x -y %d %s %s) 2> %s" % \
                        (layoutT, Renderer, Benchmarks, TimeFiles)
             Metrics = path.join(
                 etc_dir, "metrics-Layout%d-set%d-css.csv" % (layoutT, ExpNum))

tests/wpt/harness/test/test.cfg.example

@@ -8,7 +8,7 @@ ssl-type=none
 # prefs-root=/path/to/gecko-src/testing/profiles/
 
 # [servo]
-# binary=/path/to/servo-src/components/servo/target/servo
+# binary=/path/to/servo-src/target/release/servo
 # exclude=testharness # Because it needs a special testharness.js
 
 # [chrome]

tests/wpt/run.py

@@ -40,7 +40,7 @@ def set_defaults(paths, kwargs):
 
     if kwargs["binary"] is None:
         bin_dir = "release" if kwargs["release"] else "debug"
-        bin_path = servo_path("components", "servo", "target", bin_dir, "servo")
+        bin_path = servo_path("target", bin_dir, "servo")
 
         kwargs["binary"] = bin_path