fix a sign-compare warning and use -Wall

Test: mma
Bug: 34901468
Change-Id: If68c1540a88ea28987fb7359a0ee01cf45263579
diff --git a/power/1.0/default/Android.bp b/power/1.0/default/Android.bp
index 1a5a897..8bdac73 100644
--- a/power/1.0/default/Android.bp
+++ b/power/1.0/default/Android.bp
@@ -17,6 +17,11 @@
     relative_install_path: "hw",
     srcs: ["Power.cpp"],
 
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+
     shared_libs: [
         "liblog",
         "libhardware",
@@ -35,6 +40,11 @@
     init_rc: ["android.hardware.power@1.0-service.rc"],
     srcs: ["service.cpp"],
 
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
+
     shared_libs: [
         "liblog",
         "libdl",
diff --git a/power/1.0/default/Power.cpp b/power/1.0/default/Power.cpp
index 2ddac0a..6ea9167 100644
--- a/power/1.0/default/Power.cpp
+++ b/power/1.0/default/Power.cpp
@@ -81,7 +81,7 @@
     number_platform_modes = mModule->get_number_of_platform_modes(mModule);
     if (number_platform_modes)
     {
-       if (SIZE_MAX / sizeof(size_t) <= number_platform_modes)  // overflow
+       if ((ssize_t) (SIZE_MAX / sizeof(size_t)) <= number_platform_modes)  // overflow
            goto done;
        voters = new (std::nothrow) size_t [number_platform_modes];
        if (voters == nullptr)
@@ -91,7 +91,7 @@
        if (ret != 0)
            goto done;
 
-       if (SIZE_MAX / sizeof(power_state_platform_sleep_state_t)
+       if ((ssize_t) (SIZE_MAX / sizeof(power_state_platform_sleep_state_t))
            <= number_platform_modes)  // overflow
            goto done;
        legacy_states = new (std::nothrow)