gdb: disable commit-resumed on -exec-interrupt --thread-group

gdb: disable commit-resumed on -exec-interrupt --thread-group

As reported in PR gdb/28077, we hit an internal error when using
-exec-interrupt with --thread-group:

    info threads
    &"info threads\n"
    ~"  Id   Target Id             Frame \n"
    ~"* 1    process 403312 \"loop\" (running)\n"
    ^done
    (gdb)
    -exec-interrupt --thread-group i1
    ~"/home/simark/src/binutils-gdb/gdb/target.c:3768: internal-error: void target_stop(ptid_t): Assertion `!proc_target->commit_resumed_state' failed.\nA problem internal to GDB has been detected,\nfurther debugging may prove unreliable.\nQuit this debugging session? (y or n) "

This is because this code path never disables commit-resumed (a
requirement for calling target_stop, as documented in
process_stratum_target::»commit_resumed_state) before calling
target_stop.

The other 3 code paths in mi_cmd_exec_interrupt use interrupt_target_1,
which does it.  But the --thread-group code path uses its own thing
which doesn't do it.  Fix this by adding a scoped_disable_commit_resumed
in this code path.

Calling -exec-interrupt with --thread-group is apparently not tested at
the moment (which is why this bug could creep in).  Add a new test for
that.  The test runs two inferiors and tries to interrupt them with
"-exec-interrupt --thread-group X".

This will need to be merged in the gdb-11-branch, so here are ChangeLog
entries:

gdb/ChangeLog:

	* mi/mi-main.c (mi_cmd_exec_interrupt): Use
	scoped_disable_commit_resumed in the --thread-group case.

gdb/testsuite/ChangeLog:

	* gdb.mi/interrupt-thread-group.c: New.
	* gdb.mi/interrupt-thread-group.exp: New.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28077
Change-Id: I615efefcbcaf2c15d47caf5e4b9d82854b2a2fcb