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/core/clear_vars.mk b/core/clear_vars.mk
index fb775c9..e2f1444 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -182,6 +182,7 @@
 LOCAL_SANITIZE_RECOVER:=
 LOCAL_DBUS_PROXY_PREFIX:=
 LOCAL_INIT_RC:=
+LOCAL_MODULE_HOST_OS:=
 
 # arch specific variables
 LOCAL_SRC_FILES_$(TARGET_ARCH):=
diff --git a/core/module_arch_supported.mk b/core/module_arch_supported.mk
index a5e4a7c..9f05060 100644
--- a/core/module_arch_supported.mk
+++ b/core/module_arch_supported.mk
@@ -8,6 +8,8 @@
 ## LOCAL_MODULE_$(my_prefix)ARCH_WARN
 ## LOCAL_MODULE_UNSUPPORTED_$(my_prefix)ARCH
 ## LOCAL_MODULE_UNSUPPORTED_$(my_prefix)ARCH_WARN
+## LOCAL_IS_HOST_MODULE
+## LOCAL_MODULE_HOST_OS
 ##
 ## Inputs from build system:
 ## $(my_prefix)IS_64_BIT
@@ -58,3 +60,14 @@
 my_module_arch_supported := false
 $(warning $(LOCAL_MODULE): architecture $($(my_prefix)$(LOCAL_2ND_ARCH_VAR_PREFIX)ARCH) unsupported)
 endif
+
+ifdef LOCAL_IS_HOST_MODULE
+ifneq (,$(LOCAL_MODULE_HOST_OS))
+  ifeq (,$(filter $($(my_prefix)OS),$(LOCAL_MODULE_HOST_OS)))
+    my_module_arch_supported := false
+  endif
+else ifeq ($($(my_prefix)OS),windows)
+  # If LOCAL_MODULE_HOST_OS is empty, only linux and darwin are supported
+  my_module_arch_supported := false
+endif
+endif
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
 
diff --git a/tools/zipalign/Android.mk b/tools/zipalign/Android.mk
index cba6db3..8c0240a 100644
--- a/tools/zipalign/Android.mk
+++ b/tools/zipalign/Android.mk
@@ -33,5 +33,6 @@
 endif # BUILD_HOST_static
 
 LOCAL_MODULE := zipalign
+LOCAL_MODULE_HOST_OS := darwin linux windows
 
 include $(BUILD_HOST_EXECUTABLE)