sim: include stdint.h when needed

Avoid implicit include deps with this to help untangle sim headers
so we can get rid of arch-specific sim-main.h.

sim/common/callback.c

@@ -29,6 +29,7 @@
 #include <limits.h>
 #include <signal.h>
 #include <stdarg.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

sim/common/sim-io.c

@@ -27,6 +27,7 @@
 #include <fcntl.h>
 #endif
 #include <stdarg.h>
+#include <stdint.h>
 #include <stdlib.h>
 #if HAVE_UNISTD_H
 #include <unistd.h>

sim/common/sim-io.h

@@ -24,6 +24,7 @@
 #define SIM_IO_H
 
 #include <stdarg.h>
+#include <stdint.h>
 #include <sys/stat.h>
 #include <sys/types.h>