Add LOCAL_MODULE_HOST_OS

Instead of wrapping a host module definition in 'ifeq($(HOST_OS),...)'
in the Android.mk files, define which hosts are supported using
LOCAL_MODULE_HOST_OS.

A blank LOCAL_MODULE_HOST_OS means that linux and darwin are supported.
A non-empty LOCAL_MODULE_HOST_OS lists the supported HOST_OSs.

Change-Id: I1e342d1908cfa00aef2c39c145b4f5f81c373bc6
diff --git a/libs/host/Android.mk b/libs/host/Android.mk
index 8c8f755..7eb3aa1 100644
--- a/libs/host/Android.mk
+++ b/libs/host/Android.mk
@@ -7,6 +7,7 @@
 LOCAL_CFLAGS_darwin += -DMACOSX_RSRC
 
 LOCAL_MODULE:= libhost
+LOCAL_MODULE_HOST_OS := darwin linux windows
 LOCAL_C_INCLUDES := $(LOCAL_PATH)/include
 LOCAL_CXX_STL := none