Defines starting with `u' in machdep/i386

• U machdep/i386/idt.c:174
• UCODE_SEL machdep/i386/seg.h:126
• UCS_SEL machdep/i386/seg.h:187
• UDATA_SEL machdep/i386/seg.h:133
• UDS_SEL machdep/i386/seg.h:194
• UNROLL machdep/i386/fault_copy.c:42