lib: posix: Fix compile error with mqueue.h

With newer newlib we get a build error with mqueue.h realted to mode_t.
Let's just let newlib define mode_t and have minimal libc also define
it in sys/types.h.  So we remove the duplicated definition in
posix/unistd.h.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>

include/posix/mqueue.h

@@ -17,7 +17,6 @@ extern "C" {
 #endif
 
 typedef void *mqd_t;
-typedef unsigned int mode_t;
 
 typedef struct mq_attr {
 	long mq_flags;

include/posix/unistd.h

@@ -16,11 +16,6 @@ extern "C" {
 #ifdef CONFIG_POSIX_API
 #include <fs.h>
 
-#ifndef _MODE_T_DECLARED
-typedef unsigned int mode_t;
-#define _MODE_T_DECLARED
-#endif
-
 /* File related operations */
 extern int open(const char *name, int flags);
 extern int close(int file);

lib/libc/minimal/include/sys/types.h

@@ -8,6 +8,8 @@
 #ifndef ZEPHYR_LIB_LIBC_MINIMAL_INCLUDE_SYS_TYPES_H_
 #define ZEPHYR_LIB_LIBC_MINIMAL_INCLUDE_SYS_TYPES_H_
 
+typedef unsigned int mode_t;
+
 #if !defined(__ssize_t_defined)
 #define __ssize_t_defined