Added a shared memory test.

- libposix error printing now configurable via macro definition
- shmget/at/dt tested.

tasks/libposix/getpid.c

@@ -3,6 +3,7 @@
 #include <l4lib/arch/syslib.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <libposix.h>
 
 pid_t getpid(void)
 {