fsx.c: Add header file stdbool.h

Compilation failed on RHEL6.7GA because stdbool.h is not included in
xfs/platform_defs-x86_64.h or xfs/linux.h on RHEL6.7GA, so fix it.

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

ltp/fsx.c

@@ -20,6 +20,7 @@
 #include <strings.h>
 #include <sys/file.h>
 #include <sys/mman.h>
+#include <stdbool.h>
 #ifdef HAVE_ERR_H
 #include <err.h>
 #endif