When testing current gdb trunk on Solaris/amd64, the whole session was
reliably terminated by make check.  I could trace this to the following
entry in gdb.arch/amd64-disp-step/gdb.log:

FAIL: gdb.arch/amd64-disp-step.exp: add into rcx: send_signal=on: get inferior pid
Executing on target: kill -ALRM -1    (timeout = 300)
builtin_spawn -ignore SIGHUP kill -ALRM -1

If $inferior_pid doesn't refer a single process for some reason, this
kill would terminate either a process group or the whole session.

This patch avoids this by ensuring that the pid arg is positive.

Tested on amd64-pc-solaris2.11 and x86_64-pc-linux-gnu.

Ok for trunk?

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University