Only turn host build on for linux

Change-Id: I2d3b16f7881ad82cf272a40213dd4e173f54baa0
diff --git a/target/product/core.mk b/target/product/core.mk
index b7d66f2..30c77af 100644
--- a/target/product/core.mk
+++ b/target/product/core.mk
@@ -76,7 +76,9 @@
 # force WITH_HOST_DALVIK on userdebug and user builds.
 # TODO: this is redundant with a similar clause in build/core/main.mk.
 ifneq (,$(filter userdebug user,$(TARGET_BUILD_VARIANT)))
+  ifeq ($(HOST_OS),linux)
     WITH_HOST_DALVIK := true
+  endif
 endif
 
 # host-only dependencies