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.tests b/Makefile.tests
index 786f63d..badb811 100644
--- a/Makefile.tests
+++ b/Makefile.tests
@@ -5,6 +5,7 @@
   android/utils/bufprint_unittest.cpp \
   android/utils/eintr_wrapper_unittest.cpp \
   android/utils/file_data_unittest.cpp \
+  android/utils/host_bitness_unittest.cpp \
   android/utils/property_file_unittest.cpp \
   android/utils/win32_cmdline_quote_unittest.cpp \
   android/base/containers/PodVector_unittest.cpp \