osdep.h: Always include <sys/signal.h> if it exists

Regularize our handling of <sys/signal.h>: currently we include it in
osdep.h, but only for OpenBSD, and we include it without an ifdef
guard in a couple of C files.  This causes problems for Haiku, which
doesn't have that header.

Instead, check in configure whether sys/signal.h exists, and if it
does then always include it from osdep.h.

Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200703145614.16684-5-peter.maydell@linaro.org
[PMM: Expanded commit message; rename to HAVE_SYS_SIGNAL_H]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

configure

@@ -3244,6 +3244,13 @@ if check_include "libdrm/drm.h" ; then
     have_drm_h=yes
 fi
 
+#########################################
+# sys/signal.h check
+have_sys_signal_h=no
+if check_include "sys/signal.h" ; then
+  have_sys_signal_h=yes
+fi
+
 ##########################################
 # VTE probe
 
@@ -7433,6 +7440,9 @@ fi
 if test "$have_openpty" = "yes" ; then
     echo "HAVE_OPENPTY=y" >> $config_host_mak
 fi
+if test "$have_sys_signal_h" = "yes" ; then
+    echo "HAVE_SYS_SIGNAL_H=y" >> $config_host_mak
+fi
 
 # Work around a system header bug with some kernel/XFS header
 # versions where they both try to define 'struct fsxattr':

hw/xen/xen-legacy-backend.c

@@ -23,7 +23,6 @@
  */
 
 #include "qemu/osdep.h"
-#include <sys/signal.h>
 
 #include "hw/sysbus.h"
 #include "hw/boards.h"

include/qemu/osdep.h

@@ -104,7 +104,7 @@ extern int daemon(int, int);
 #include <setjmp.h>
 #include <signal.h>
 
-#ifdef __OpenBSD__
+#ifdef HAVE_SYS_SIGNAL_H
 #include <sys/signal.h>
 #endif
 

util/oslib-posix.c

@@ -38,7 +38,6 @@
 #include "qemu/sockets.h"
 #include "qemu/thread.h"
 #include <libgen.h>
-#include <sys/signal.h>
 #include "qemu/cutils.h"
 
 #ifdef CONFIG_LINUX