linux-user: Split signal-related prototypes into signal-common.h

Split the signal related prototypes into the existing header file
signal-common.h, and include it in those places that now require it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210908154405.15417-4-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 4ac2801..ad635ed 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -128,6 +128,7 @@
 
 #include "qemu.h"
 #include "strace.h"
+#include "signal-common.h"
 #include "qemu/guest-random.h"
 #include "qemu/selfmap.h"
 #include "user/syscall-trace.h"