c/89270 - honor registered_builtin_types in type_for_size

c/89270 - honor registered_builtin_types in type_for_size

The following fixes the intermediate conversions inserted by
convert_to_integer when facing address-spaces and converts
to their effective [u]intptr_t when they are registered_builtin_types
by considering those also from c_common_type_for_size and not
only from c_common_type_for_mode.

	PR c/89270
gcc/c-family/
	* c-common.cc (c_common_type_for_size): Consider
	registered_builtin_types.

gcc/testsuite/
	* gcc.target/avr/pr89270.c: New testcase.