Add AM_PROG_CC_C_O to configure.am
As advised by the following warning:

automake (GNU automake) 1.10.1
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv2+: GNU GPL version 2 or later http://gnu.org/licenses/gpl.html
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Tom Tromey <tromey@redhat.com>

and Alexandre Duret-Lutz <adl@gnu.org>.

heartbeat/Makefile.am:57: compiling heartbeat.c' with per-target flags requires AM_PROG_CC_C_O' in `configure.in'

Signed-off-by: Simon Horman <horms@verge.net.au>

--HG--
extra : convert_revision : a4431b4f174920a198b60c1e11ed2da2fb531f5d