Sync linker with internal branch

This change includes dlwarning implementation and
the compatibility greylist for apps targeting pre-N.

Change-Id: Ibf02a07cc58cbbb1a5aef4ac34558c5d43e4305f
Test: Run bionic-unit-tests --gtest_filter=dl*:Dl*
diff --git a/libdl/libdl.map.txt b/libdl/libdl.map.txt
index 79bced3..962692e 100644
--- a/libdl/libdl.map.txt
+++ b/libdl/libdl.map.txt
@@ -35,6 +35,7 @@
 
 LIBC_PLATFORM {
   global:
+    android_dlwarning;
     android_get_application_target_sdk_version;
     android_set_application_target_sdk_version;
     android_get_LD_LIBRARY_PATH;