i386: Fix -mcmodel= vs. target attribute [PR98585]

i386: Fix -mcmodel= vs. target attribute [PR98585]

My patch to save/restore opts_set rather than essentially treating
global_options_set as a logical or whether some option has ever been
explicitly set somewhere apparently broke -mcmodel= vs. target attribute
(and as the patch shows some other options too).
The thing is, at least for options for which we ever test opts_set->x_*
or global_options_set.x_*, we need to save/restore them next to the
saving/restoring of the actual option values.
If an option has Save keyword or in case of TargetVariable, it is the
generic code that handles the saving and restoring of both the option
and corresponding opts_set flag automatically, for other variables
(TargetSave, or Target without Save) the backend needs to do that in the
target hook manually and in that case should save/restore both the option
values (the hooks mostly did that) and opts_set (they didn't).

As it seems much easier to let the automatic saving/restoring do the work
for us unless the saving/restoring of the option needs some specific magic,
the following patch is a result of grepping through the backend for
opts_set->x_ and global_options_set.x_ and for all such referenced
variables, grepping whether it is saved/restored including opts_set properly
in the generated options-save.c or not.

2021-01-08  Jakub Jelinek  <jakub@redhat.com>

	PR target/98585
	* config/i386/i386.opt (ix86_cmodel, ix86_incoming_stack_boundary_arg,
	ix86_pmode, ix86_preferred_stack_boundary_arg, ix86_regparm,
	ix86_veclibabi_type): Remove x_ prefix, use TargetVariable instead of
	TargetSave and initialize for variables with enum types.
	(mfentry, mstack-protector-guard-reg=, mstack-protector-guard-offset=,
	mstack-protector-guard-symbol=): Add Save.
	* config/i386/i386-options.c (ix86_function_specific_save,
	ix86_function_specific_restore): Don't save or restore x_ix86_cmodel,
	x_ix86_incoming_stack_boundary_arg, x_ix86_pmode,
	x_ix86_preferred_stack_boundary_arg, x_ix86_regparm,
	x_ix86_veclibabi_type.

	* gcc.target/i386/pr98585.c: New test.