Auto merge of #11122 - mbrubeck:unify-builds, r=larsbergstrom

Use the same build environment and features for CEF, Servo, Gonk, Geckolib

* Remove unnecessary dependencies and features from top-level Cargo.tomls.  The features for each crate will be computed based on the union of features specified in the dependency graph.  Specifying the same ones again just adds more ways for them to get out of sync.
* Move all cargo build environment variables into CommandBase

Fixes #11112. r? @metajack

(Not included: CI test to make sure #11112 doesn't regress again.)

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python/servo/command_base.py

@@ -256,7 +256,7 @@ class CommandBase(object):
                                   " --release" if release else ""))
         sys.exit()
 
-    def build_env(self, gonk=False, hosts_file_path=None):
+    def build_env(self, gonk=False, hosts_file_path=None, target=None):
         """Return an extended environment dictionary."""
         env = os.environ.copy()
         if sys.platform == "win32" and type(env['PATH']) == unicode:
@@ -400,6 +400,16 @@ class CommandBase(object):
             if subprocess.call(['which', 'ld.gold'], stdout=PIPE, stderr=PIPE) == 0:
                 env['RUSTFLAGS'] = env.get('RUSTFLAGS', "") + " -C link-args=-fuse-ld=gold"
 
+        if not (self.config["build"]["ccache"] == ""):
+            env['CCACHE'] = self.config["build"]["ccache"]
+
+        # Ensure Rust uses hard floats and SIMD on ARM devices
+        if target:
+            if target.startswith('arm') or target.startswith('aarch64'):
+                env['RUSTFLAGS'] = env.get('RUSTFLAGS', "") + " -C target-feature=+neon"
+
+        env['RUSTFLAGS'] = env.get('RUSTFLAGS', "") + " -W unused-extern-crates"
+
         return env
 
     def servo_crate(self):