Displaced stepping on ARM has been supported for a while, but there is
no testcase for it.

arm-disp-step.S can be compiled in both Thumb and ARM, so it can be used
for thumb displaced stepping when Thumb displaced stepping is supported
in the future.

arm-disp-step.exp will xfail when arm-disp-step.S is compiled in Thumb
mode.  Once GDB supports Thumb displaced stepping, we can remove it.

Run arm-disp-step.exp with
\{-mthumb,-marm\}\{-march=armv5t,-march=armv7-a\}, get result like this,
		=== gdb Summary ===

# of expected passes		60
# of expected failures		2

OK to apply?

-- 
Yao (齐尧)