[binutils-gdb] Use enum for return method for dummy calls

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT c5ac5cbb5be91d43bd31ac0068917bdb7ab9b439 ***

Author: Alan Hayward <alan.hayward@arm.com>
Branch: master
Commit: c5ac5cbb5be91d43bd31ac0068917bdb7ab9b439

Use enum for return method for dummy calls

In call_function_by_hand_dummy, struct_return and hidden_first_param_p
are used to represent a single concept. Replace with an enum.

gdb/ChangeLog:

	* gdbarch.sh (enum function_call_return_method): Add enum.
	* gdbarch.h: Regenerate.
	* infcall.c (call_function_by_hand_dummy): Replace vars with enum.