During reviewing "arm reverse debugging" patch, we realize that tests in
gdb.reverse are not run in common regression test unless we set some
variables in board file.

This patch is to convert variable checking in each reverse test case to
a proc return value checking, so that gdb.reverse tests will be run on
targets that support reverse debugging.

Run gdb.reverse on x86-linux, and get follow result,

FAIL: gdb.reverse/solib-precsave.exp: reverse-step third sleep
FAIL: gdb.reverse/solib-precsave.exp: reverse-step second sleep
FAIL: gdb.reverse/solib-precsave.exp: reverse-step first sleep, dynsym
resolve
FAIL: gdb.reverse/solib-precsave.exp: reverse-step third printf
FAIL: gdb.reverse/solib-precsave.exp: reverse-step second printf
FAIL: gdb.reverse/solib-precsave.exp: reverse-step first printf, dynsym
resolve
FAIL: gdb.reverse/solib-precsave.exp: reverse-step generic
FAIL: gdb.reverse/solib-precsave.exp: reverse-next third sleep
FAIL: gdb.reverse/solib-precsave.exp: reverse-next second sleep
FAIL: gdb.reverse/solib-precsave.exp: reverse-next first sleep, dynsym
resolve
FAIL: gdb.reverse/solib-precsave.exp: reverse-next third printf
FAIL: gdb.reverse/solib-precsave.exp: reverse-next second printf
FAIL: gdb.reverse/solib-precsave.exp: reverse-next first printf, dynsym
resolve
FAIL: gdb.reverse/solib-precsave.exp: reverse-next generic
FAIL: gdb.reverse/solib-precsave.exp: reverse-step into solib function one
FAIL: gdb.reverse/solib-precsave.exp: reverse-step within solib function one
FAIL: gdb.reverse/solib-precsave.exp: reverse-step back to main one
FAIL: gdb.reverse/solib-precsave.exp: reverse-step into solib function two
FAIL: gdb.reverse/solib-precsave.exp: reverse-step within solib function two
FAIL: gdb.reverse/solib-precsave.exp: reverse-step back to main two
FAIL: gdb.reverse/solib-precsave.exp: reverse-next over solib function one
FAIL: gdb.reverse/solib-precsave.exp: reverse-next over solib function two
		=== gdb Summary ===

# of expected passes		2774
# of unexpected failures	22

I didn't KFAIL them, because the reason of fails are unknown to me.  OK
to apply?

-- 
Yao (齐尧)