fix some src compile problems

Index: src/skins/posix/clock.c
===================================================================
@@ -16,6 +16,8 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
  */
 
+#include <stdio.h>
+#include <stdlib.h>
 #include <errno.h>
 #include <pthread.h>		/* For pthread_setcanceltype. */
 #include <posix/syscall.h>

Index: src/skins/native/timer.c
===================================================================
@@ -16,6 +16,8 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
  */
 
+#include <stdio.h>
+#include <stdlib.h>
 #include <native/syscall.h>
 #include <native/timer.h>
 #include <asm/xenomai/arith.h>

Index: src/testsuite/clocktest/clocktest.c
===================================================================
@@ -160,7 +160,7 @@ int main(int argc, char *argv[])
 {
     int cpus = sysconf(_SC_NPROCESSORS_ONLN);
     int i;
-    char c;
+    int c;
 
     while ((c = getopt(argc,argv,"C:T:")) != EOF)
         switch (c) {