android/utils/host_bitness.c: android_getHostBitness()

This patch moves the host bitness detection code to android/utils/
and also improves it to work properly on Windows, in preparation for
Win64 executables.

+ Ensure 'emulator' launcher uses it.
+ Add basic unit test.

Change-Id: I7d55397efeb749b72c502241c4da4cd16696c082
diff --git a/Makefile.common b/Makefile.common
index 1b1e4b6..3f60621 100644
--- a/Makefile.common
+++ b/Makefile.common
@@ -135,6 +135,7 @@
 	android/utils/eintr_wrapper.c \
 	android/utils/filelock.c \
 	android/utils/file_data.c \
+	android/utils/host_bitness.c \
 	android/utils/ini.c \
 	android/utils/intmap.c \
 	android/utils/lineinput.c \