Add API to set page size compat mode

Adding APIs in libdl to set linker global which will be used to set the page size compat mode for particular app.

Test: atest bionic-unit-tests
Test: atest CtsBionicTestCases
Bug: 371049373

Change-Id: I20f0fe9ece5db833568edf27ec268edf999f1741
diff --git a/linker/linker.h b/linker/linker.h
index ac2222d..a2424c6 100644
--- a/linker/linker.h
+++ b/linker/linker.h
@@ -108,6 +108,9 @@
 
 bool get_transparent_hugepages_supported();
 
+void set_16kb_appcompat_mode(bool enable_app_compat);
+bool get_16kb_appcompat_mode();
+
 enum {
   /* A regular namespace is the namespace with a custom search path that does
    * not impose any restrictions on the location of native libraries.