TEQ with S bit = 0 would be pointless, so ARM uses this case to encode "miscellaneous"
instructions like BKPT, BX and BLX.  Decoding these correctly allows db/acid to
single step through BX and BLX on armv5t+, and to show a breakpoint instruction
as 'BKPT $#0' instead of 'TEQ R0@>R0,R0'.