X86: reverse-finish fix

X86: reverse-finish fix

PR record/29927  - reverse-finish requires two reverse next instructions to
reach previous source line

Currently on X86, when executing the finish command in reverse, gdb does a
single step from the first instruction in the callee to get back to the
caller.  GDB stops on the last instruction in the source code line where
the call was made.  When stopped at the last instruction of the source code
line, a reverse next or step command will stop at the first instruction
of the same source code line thus requiring two step/next commands to
reach the previous source code line.  It should only require one step/next
command to reach the previous source code line.

By contrast, a reverse next or step command from the first line in a
function stops at the first instruction in the source code line where the
call was made.

This patch fixes the reverse finish command so it will stop at the first
instruction of the source line where the function call was made.  The
behavior on X86 for the reverse-finish command now matches doing a
reverse-next from the beginning of the function.

The proceed_to_finish flag in struct thread_control_state is no longer
used.  This patch removes the declaration, initialization and setting of
the flag.

This patch requires a number of regression tests to be updated.  Test
gdb.mi/mi-reverse.exp no longer needs to execute two steps to get to the
previous line.  The gdb output for tests gdb.reverse/until-precsave.exp
and gdb.reverse/until-reverse.exp changed slightly.  The expected result in
tests gdb.reverse/amd64-failcall-reverse.exp and
gdb.reverse/singlejmp-reverse.exp are updated to the correct expected
result.

This patch adds a new test gdb.reverse/finish-reverse-next.exp to test the
reverse-finish command when returning from the entry point and from the
body of the function.

The step_until proceedure in test gdb.reverse/step-indirect-call-thunk.exp
was moved to lib/gdb.exp and renamed cmd_until.

The patch has been tested on X86 and PowerPC to verify no additional
regression failures occured.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29927