ARC: MWDT: LIB: implement _istty hook

Implement _istty hook as it is required for proper setup of
STDIN/STDOUT/STDERR buffering.

Signed-off-by: Eugeniy Paltsev <[email protected]>
Signed-off-by: Evgeniy Paltsev <[email protected]>

Author: evgeniy-paltsev

lib/libc/arcmwdt/libc-hooks.c

@@ -10,6 +10,7 @@
 #include <syscall_handler.h>
 #include <string.h>
 #include <sys/errno_private.h>
+#include <unistd.h>
 #include <errno.h>
 
 static int _stdout_hook_default(int c)
@@ -58,6 +59,19 @@ int _write(int fd, const char *buf, unsigned int nbytes)
 }
 #endif
 
+/*
+ * It's require to implement _isatty to have STDIN/STDOUT/STDERR buffered
+ * properly.
+ */
+int _isatty(int file)
+{
+	if (file == STDIN_FILENO || file == STDOUT_FILENO || file == STDERR_FILENO) {
+		return 1;
+	}
+
+	return 0;
+}
+
 int *___errno(void)
 {
 	return z_errno();