libui: 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: I470a267e9b1c373f2d5c960f005c3b0e02b2db63
diff --git a/include/ui/PixelFormat.h b/include/ui/PixelFormat.h
index 7e46945..e7e8ffc 100644
--- a/include/ui/PixelFormat.h
+++ b/include/ui/PixelFormat.h
@@ -25,9 +25,6 @@
 #ifndef UI_PIXELFORMAT_H
 #define UI_PIXELFORMAT_H
 
-#include <stdint.h>
-#include <sys/types.h>
-#include <utils/Errors.h>
 #include <hardware/hardware.h>
 
 namespace android {
@@ -69,8 +66,8 @@
 
 typedef int32_t PixelFormat;
 
-ssize_t bytesPerPixel(PixelFormat format);
-ssize_t bitsPerPixel(PixelFormat format);
+uint32_t bytesPerPixel(PixelFormat format);
+uint32_t bitsPerPixel(PixelFormat format);
 
 }; // namespace android