Fix uninitialized variable warnings.

Fix uninitialized variable warnings.

Check for use of previously uninitialized variables; call gcc_unreachable().
Replace abort() with gcc_unreachable().

2022-10-22  Michael Eager  <eager@eagercon.com>

gcc/
	* config/microblaze/microblaze.cc
	(microblaze_legitimize_address): Initialize 'reg' to NULL, check for NULL.
	(microblaze_address_insns): Replace abort() with gcc_unreachable().
	(print_operand_address): Same.
	(microblaze_expand_move): Initialize 'p1' to NULL, check for NULL.
	(get_branch_target): Replace abort() with gcc_unreachable().