Mark (BUILD_|LOCAL_)COPY_HEADERS as [more] deprecated

We've considered these deprecated for a while, and have reduced where
they may be used, but let's actually throw warnings and call them out
specifically now.

Bug: 130719878
Test: lunch aosp_arm; m nothing   [see no warnings]
Test: lunch aosp_crosshatch; m nothing   [see LOCAL_COPY_HEADERS warnings]
Test: lunch aosp_taimen; m nothing  [see BUILD_COPY_HEADERS warnings]
Change-Id: I8c12012366d84667de0d223bbde38d8b90419e36
diff --git a/core/host_shared_library.mk b/core/host_shared_library.mk
index 81236d1..c22af97 100644
--- a/core/host_shared_library.mk
+++ b/core/host_shared_library.mk
@@ -37,4 +37,7 @@
 ###########################################################
 ## Copy headers to the install tree
 ###########################################################
-include $(BUILD_COPY_HEADERS)
+ifdef LOCAL_COPY_HEADERS
+$(call pretty-warning,LOCAL_COPY_HEADERS is deprecated. See $(CHANGES_URL)#copy_headers)
+include $(BUILD_SYSTEM)/copy_headers.mk
+endif