Defines starting with `u' in mint

• UNDEF mint/bios.c:19
• UNDO mint/bios.c:24
• UNIDRV mint/file.h:677
• UNI_NUM_DRVS mint/file.h:676
• UNK_RDEV mint/file.h:686
• UNLIMITED mint/file.h:404
• UNMASKABLE mint/signal.h:41