Replace ANDROID with __ANDROID__ (#4909)

__ANDROID__ is always set by the toolchain and less likely to cause
conflicts than ANDROID. This change also removes the -DANDROID flag
we set ourselves in our toolchain CMake files since we don't need
it anymore.

libs/utils/src/api_level.cpp

@@ -19,14 +19,14 @@
 
 #include <utils/api_level.h>
 
-#ifdef ANDROID
+#ifdef __ANDROID__
 #include <mutex>
 #include <sys/system_properties.h>
 #endif
 
 namespace utils {
 
-#ifdef ANDROID
+#ifdef __ANDROID__
 
 uint32_t sApiLevel = 0;
 std::once_flag sApiLevelOnceFlag;