gdb: Remove a non-const reference parameter

gdb: Remove a non-const reference parameter

Non-const reference parameter should be avoided according to the GDB
coding standard:

  https://sourceware.org/gdb/wiki/Internals%20GDB-C-Coding-Standards#Avoid_non-const_reference_parameters.2C_use_pointers_instead

This commit updates the gdbarch method gdbarch_stap_adjust_register,
and the one implementation i386_stap_adjust_register to avoid using a
non-const reference parameter.

I've also removed the kfail from the testsuite for bug 24541, as this
issue is now resolved.

gdb/ChangeLog:

	PR breakpoints/24541
	* gdbarch.c: Regenerate.
	* gdbarch.h: Regenerate.
	* gdbarch.sh: Adjust return type and parameter types for
	'stap_adjust_register'.
	(i386_stap_adjust_register): Adjust signature and return new
	register name.
	* stap-probe.c (stap_parse_register_operand): Adjust use of
	'gdbarch_stap_adjust_register'.

gdb/testsuite/ChangeLog:

	PR breakpoints/24541
	* gdb.mi/mi-catch-cpp-exceptions.exp: Remove kfail due to 24541.