Only bother building the host tests for Linux.

It's the only place you can run the host tests anyway.

Change-Id: I5fe2b5b74e70a17696baf8ceaacaf4fca52d71ca
diff --git a/JavaLibrary.mk b/JavaLibrary.mk
index c857390..9670d1b 100644
--- a/JavaLibrary.mk
+++ b/JavaLibrary.mk
@@ -148,6 +148,8 @@
 # Build for the host.
 #
 
+ifeq ($(HOST_OS),linux)
+
 include $(CLEAR_VARS)
 LOCAL_SRC_FILES := $(call all-main-java-files-under, dex)
 LOCAL_MODULE_TAGS := optional
@@ -199,6 +201,8 @@
     include $(BUILD_HOST_DALVIK_JAVA_LIBRARY)
 endif
 
+endif # HOST_OS == linux
+
 #
 # Local droiddoc for faster libcore testing
 #