* i386.h: Declare ix86_cpu_string, ix86_arch_string,
i386_reg_alloc_order, i386_regparm_string,
i386_align_loops_string, i386_align_jumps_string,
i386_align_funcs_string, i386_preferred_stack_boundary_string,
and i386_branch_cost_string as type "const char *".
* i386.c: Define all above strings as type "const char *".