libdl: Rename LIBC_PRIVATE to LIBC_PLATFORM

Bug: http://b/26386014
Change-Id: I3255faac66a96867aed302e205e3644b40ce7750
diff --git a/libdl/libdl.map.txt b/libdl/libdl.map.txt
index 55a03cb..67ff64e 100644
--- a/libdl/libdl.map.txt
+++ b/libdl/libdl.map.txt
@@ -35,7 +35,7 @@
     dlvsym;
 } LIBC;
 
-LIBC_PRIVATE {
+LIBC_PLATFORM {
   global:
     android_get_application_target_sdk_version;
     android_set_application_target_sdk_version;