Mark __jit_debug_register_code as a unique symbol

This symbol is used to notify the debugger about JIT library load/unload
events. Because of ICF, several functions with the same body put to the
same adress by the linker what causes the debugger to get notifictaion
about JIT load/unload events in several case where it isn't really happened.

This change disable ICF for the __jit_debug_register_code symbol to prevent
this behavior with keeping the symbol unique in the object file.

This is the 3rd attemp to mark the __jit_debug_register_code symbol unique
as the previous 2 failed because of some confilict with unrelated changes.

Tracking bug for making the same change for aarch64 after we switch to gold
there: b/26149442

Change-Id: I6edc45f27d5e57a66fb9d98c32a081f711565810