main-loop: Add missing include file

stdint.h defines the POSIX data types and is needed
for MinGW-w64 (and maybe other hosts).

v2: Instead of adding stdint.h directly, qemu-common.h is now
included and duplicate include statements were removed.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
