Fix Mac build.

Change-Id: I4d389d7050970d8fd460a4238e8c2963211780b4
diff --git a/verity/Android.mk b/verity/Android.mk
index bbe74bb..1d0574f 100644
--- a/verity/Android.mk
+++ b/verity/Android.mk
@@ -1,5 +1,7 @@
 LOCAL_PATH:= $(call my-dir)
 
+ifeq ($(HOST_OS),linux)
+
 include $(CLEAR_VARS)
 LOCAL_MODULE := verify_boot_signature
 LOCAL_SRC_FILES := verify_boot_signature.c
@@ -101,3 +103,5 @@
 LOCAL_SHARED_LIBRARIES := libcrypto-host libbase
 LOCAL_CFLAGS += -Wall -Werror
 include $(BUILD_HOST_EXECUTABLE)
+
+endif # HOST_OS == linux