This fixes the build to always define the ANDROID macro, and remove an empty -I from the compiler options.

The latter had the effect of removing the benefit of optimization settings, i.e. a typical compiler
command would look like:

   <toolchain-compiler> .... -Isources/<module-path> -I -O2 -g

The "-I -O2" was interpreted literally as "search in '-O2' directory, and the optimization was
never set to 2 (or 0 in case of debug mode).

ndk/build/core/build-binary.mk

@@ -29,6 +29,10 @@ include $(BUILD_SYSTEM)/build-module.mk
 # list of generated object files
 LOCAL_OBJECTS :=
 
+# always define ANDROID when building binaries
+#
+LOCAL_CFLAGS := -DANDROID $(LOCAL_CFLAGS)
+
 #
 # Add the default system shared libraries to the build
 #