random-sig randomly failing with gdbserver

[Philippe Waroquiers <philippe.waroquiers@skynet.be>]

gdb.base/random-sig.exp (frequently) randomly fails when running with gdbserver,
when running multiple times
  make check RUNTESTFLAGS="--target_board native-gdbserver random-signal.exp"
It looks like it can fail for at least three reasons

A successful run gives:
  (gdb) PASS: gdb.base/random-signal.exp: watch v
  continue
  Continuing.
  PASS: gdb.base/random-signal.exp: continue
  ^C
  Program received signal SIGINT, Interrupt.
  main () at ./gdb.base/random-signal.c:28
  28	    ;
  (gdb) PASS: gdb.base/random-signal.exp: stop with control-c

A failing run gives:
  (gdb) PASS: gdb.base/random-signal.exp: watch v
  continue
  Continuing.
  PASS: gdb.base/random-signal.exp: continue
  ^Cmain () at ./gdb.base/random-signal.c:28
  28	    ;
  Quit
  (gdb) FAIL: gdb.base/random-signal.exp: stop with control-c
  testcase ./gdb.base/random-signal.exp completed in 1 seconds


It can also fail with:
  (gdb) PASS: gdb.base/random-signal.exp: watch v
  continue
  Continuing.
  PASS: gdb.base/random-signal.exp: continue
  ^CFAIL: gdb.base/random-signal.exp: stop with control-c (timeout)
  testcase ./gdb.base/random-signal.exp completed in 11 seconds

Or fail with
  (gdb) PASS: gdb.base/random-signal.exp: watch v
  continue
  Continuing.
  PASS: gdb.base/random-signal.exp: continue
  ^CError evaluating expression for watchpoint 2
  Quit
  Watchpoint 2 deleted.
  main () at ./gdb.base/random-signal.c:28
  28	    ;
  (gdb) FAIL: gdb.base/random-signal.exp: stop with control-c
  testcase ./gdb.base/random-signal.exp completed in 1 seconds


Unclear what exactly happens. I suspect a race condition between
gdbserver reporting that the inferior stopped (to examine the
software watchpoint) and gdb sending at the same time
the interrupt, and expecting a SIGINT, but instead receiving
the stopped condition from gdbserver.

Philippe