i386: Fix up ix86_abi handling [PR106875]

i386: Fix up ix86_abi handling [PR106875]

The following testcase fails since my changes to make also
opts_set saved/restored upon function target/optimization changes
(before it has been acting as "has this option be ever explicit
anywhere?").

The problem is that for ix86_abi we depend on the opts_set
value for it in ix86_option_override_internal:
  SET_OPTION_IF_UNSET (opts, opts_set, ix86_abi, DEFAULT_ABI);
but as it is a TargetSave, the backend code is required to
save/restore it manually (it does that) and since gcc 11 also
to save/restore the opts_set bit for it (which isn't done).
We don't do that for various other TargetSave which
ix86_function_specific_{save,restore} saves/restores, but as long
as we never test opts_set for it, it doesn't really matter.
One possible fix would be to introduce some new TargetSave into
which ix86_function_specific_{save,restore} would save/restore a bitmask
of the opts_set bits.  The following patch uses an easier fix, by
making it a TargetVariable instead the saving/restoring is handled
by the generated code.
The differences in options.h are just slight movements on where
*ix86_abi stuff appears in it, ditto for options.cc, the real
differences are just in options-save.cc, where cl_target_option_save
gets:
+  ptr->x_ix86_abi = opts->x_ix86_abi;
...
+  if (opts_set->x_ix86_abi) mask |= HOST_WIDE_INT_1U << 3;
(plus adjustments of following TargetVariables mask related stuff),
cl_target_option_restore gets:
+  opts->x_ix86_abi = ptr->x_ix86_abi;
...
+  opts_set->x_ix86_abi = static_cast<enum calling_abi>((mask & 1) != 0);
+  mask >>= 1;
plus the movements in other functions too.  So, by it being a
TargetVariable, the only thing that changed is that we don't need to
handle it manually in ix86_function_specific_{save,restore} because it
is handled automatically including the opts_set stuff.

2022-11-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/106875
	* config/i386/i386.opt (x_ix86_abi): Remove TargetSave.
	(ix86_abi): Replace it with TargetVariable.
	* config/i386/i386-options.cc (ix86_function_specific_save,
	ix86_function_specific_restore): Don't save and restore x_ix86_abi.

	* g++.target/i386/pr106875.C: New test.