isatty() should be prototypes in unstid.h, not termios.h.

include/termios.h

@@ -298,9 +298,6 @@ int tcsendbreak(int fd, int duration);
 
 int tcsetattr(int fd, int options, FAR const struct termios *termiosp);
 
-/* Check if a file descriptor corresponds to a terminal I/O file */
-
-int isatty(int fd);
 
 #undef EXTERN
 #ifdef __cplusplus

include/unistd.h

@@ -165,6 +165,10 @@ ssize_t write(int fd, FAR const void *buf, size_t nbytes);
 ssize_t pread(int fd, FAR void *buf, size_t nbytes, off_t offset);
 ssize_t pwrite(int fd, FAR const void *buf, size_t nbytes, off_t offset);
 
+/* Check if a file descriptor corresponds to a terminal I/O file */
+
+int     isatty(int fd);
+
 /* Memory management */
 
 #if defined(CONFIG_ARCH_ADDRENV) && defined(CONFIG_MM_PGALLOC) && \