use restrict everywhere it's required by c99 and/or posix 2008

to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.

src/mq/mq_setattr.c

@@ -1,7 +1,7 @@
 #include <mqueue.h>
 #include "syscall.h"
 
-int mq_setattr(mqd_t mqd, const struct mq_attr *new, struct mq_attr *old)
+int mq_setattr(mqd_t mqd, const struct mq_attr *restrict new, struct mq_attr *restrict old)
 {
 	return syscall(SYS_mq_getsetattr, mqd, new, old);
 }

src/mq/mq_timedreceive.c

@@ -1,7 +1,7 @@
 #include <mqueue.h>
 #include "syscall.h"
 
-ssize_t mq_timedreceive(mqd_t mqd, char *msg, size_t len, unsigned *prio, const struct timespec *at)
+ssize_t mq_timedreceive(mqd_t mqd, char *restrict msg, size_t len, unsigned *restrict prio, const struct timespec *restrict at)
 {
 	return syscall_cp(SYS_mq_timedreceive, mqd, msg, len, prio, at);
 }