Fix the following warning by including signal.h directly in qemu-common.h
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iohandler.c: In function ‘qemu_init_child_watch’:
iohandler.c:172: warning: implicit declaration of function ‘sigaction’
iohandler.c:172: warning: nested extern declaration of ‘sigaction’
----8<----
Signed-off-by: NAlexandre Raymond <cerbere@gmail.com>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>