posix: unistd.h: open() doesn't belong here

Per POSIX, open() is defined in <fcntl.h>. fcntl.h in turn comes from
the underlying libc, either newlib, or minimal libc.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>

include/posix/unistd.h

@@ -21,7 +21,6 @@ extern "C" {
 #include <fs/fs.h>
 
 /* File related operations */
-extern int open(const char *name, int flags);
 extern int close(int file);
 extern ssize_t write(int file, const void *buffer, size_t count);
 extern ssize_t read(int file, void *buffer, size_t count);

lib/libc/minimal/include/fcntl.h

@@ -15,4 +15,6 @@
 #define F_GETFL 3
 #define F_SETFL 4
 
+int open(const char *name, int flags);
+
 #endif /* ZEPHYR_LIB_LIBC_MINIMAL_INCLUDE_SYS_FCNTL_H_ */

tests/posix/common/src/mqueue.c

@@ -7,6 +7,7 @@
 #include <ztest.h>
 #include <zephyr.h>
 #include <sys/printk.h>
+#include <fcntl.h>
 #include <mqueue.h>
 #include <pthread.h>
 

tests/posix/fs/src/test_fs_dir.c

@@ -5,6 +5,7 @@
  */
 
 #include <stdio.h>
+#include <fcntl.h>
 #include <posix/unistd.h>
 #include <posix/dirent.h>
 #include "test_fs.h"

tests/posix/fs/src/test_fs_file.c

@@ -5,6 +5,7 @@
  */
 
 #include <string.h>
+#include <fcntl.h>
 #include <posix/unistd.h>
 #include "test_fs.h"