libgui: Enable -Weverything and -Werror

Enables -Weverything and -Werror, with just a few exceptions for
warnings we can't (or shouldn't need to) work around.

Change-Id: I034abec27bf4020d84af60d7acc1939c59986dd6
diff --git a/libs/gui/SensorManager.cpp b/libs/gui/SensorManager.cpp
index 17960ff..d6df404 100644
--- a/libs/gui/SensorManager.cpp
+++ b/libs/gui/SensorManager.cpp
@@ -90,7 +90,8 @@
 
         mSensors = mSensorServer->getSensorList();
         size_t count = mSensors.size();
-        mSensorList = (Sensor const**)malloc(count * sizeof(Sensor*));
+        mSensorList =
+                static_cast<Sensor const**>(malloc(count * sizeof(Sensor*)));
         for (size_t i=0 ; i<count ; i++) {
             mSensorList[i] = mSensors.array() + i;
         }
@@ -106,10 +107,10 @@
     Mutex::Autolock _l(mLock);
     status_t err = assertStateLocked();
     if (err < 0) {
-        return ssize_t(err);
+        return static_cast<ssize_t>(err);
     }
     *list = mSensorList;
-    return mSensors.size();
+    return static_cast<ssize_t>(mSensors.size());
 }
 
 Sensor const* SensorManager::getDefaultSensor(int type)