untyped calls: enable target switching [PR112334]

The computation of apply_args_size and apply_result_size is saved in a
static variable, so that the corresponding _mode arrays are
initialized only once.  That is not compatible with switchable
targets, and ARM's arm_set_current_function, by saving and restoring
target globals, exercises this problem with a testcase such as that in
the PR, in which more than one function in the translation unit calls
__builtin_apply or __builtin_return, respectively.

This patch moves the _size statics into the target_builtins array,
with a bit of ugliness over _plus_one so that zero initialization of
the struct does the right thing.


for  gcc/ChangeLog

	PR target/112334
	* builtins.h (target_builtins): Add fields for apply_args_size
	and apply_result_size.
	* builtins.cc (apply_args_size, apply_result_size): Cache
	results in fields rather than in static variables.
	(get_apply_args_size, set_apply_args_size): New.
	(get_apply_result_size, set_apply_result_size): New.