Add support for AArch64 XOM binaries.

Adds build system support for generating AArch64 binaries with
execute-only memory layouts via a new LOCAL_XOM property. Also adds
support for an ENABLE_XOM build flag for global builds.

Bug: 77958880
Test: make -j ENABLE_XOM=true
Change-Id: I6af9e3615d0a9fdff802eae50e6ad94311ec8046
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 64caa18..0417e13 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -302,6 +302,7 @@
 LOCAL_VTS_MODE:=
 LOCAL_WARNINGS_ENABLE:=
 LOCAL_WHOLE_STATIC_LIBRARIES:=
+LOCAL_XOM:=
 LOCAL_YACCFLAGS:=
 # TODO: deprecate, it does nothing
 OVERRIDE_BUILT_MODULE_PATH:=