Allow 'export WITH_HOST_DALVIK=false' to override Makefile defaulting

Change-Id: I8915bc1c9f52a3b6ab1a82b404ab61cd0726198d
diff --git a/core/envsetup.mk b/core/envsetup.mk
index f556efe..72c7961 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -119,12 +119,16 @@
   HOST_PREBUILT_TAG := $(HOST_OS)-$(HOST_ARCH)
 endif
 
-# Build dalvikvm on hosts that support it, but not if we're building the sim
+# Default to building dalvikvm on hosts that support it...
 ifeq ($(HOST_OS),linux)
+# ... but not if we're building the sim...
 ifneq ($(TARGET_SIMULATOR),true)
+# ... or if the if the option is already set
+ifeq ($(WITH_HOST_DALVIK),)
 	WITH_HOST_DALVIK := true
 endif
 endif
+endif
 
 
 # ---------------------------------------------------------------