Compile bit on darwin, use -j when invoking make

Test: ran the host tool and checked the output
Change-Id: Idd561139348779982b8c01977fcc18fdfbd0134d
diff --git a/tools/bit/Android.mk b/tools/bit/Android.mk
index 1c1291f..57f46d4 100644
--- a/tools/bit/Android.mk
+++ b/tools/bit/Android.mk
@@ -22,8 +22,7 @@
 
 LOCAL_MODULE := bit
 
-# This tool doesn't build on darwin.
-LOCAL_MODULE_HOST_OS := linux
+LOCAL_MODULE_HOST_OS := linux darwin
 
 LOCAL_SRC_FILES := \
     aapt.cpp \
@@ -43,4 +42,3 @@
     libprotobuf-cpp-full
 
 include $(BUILD_HOST_EXECUTABLE)
-