suppress warnings

* string.c (rb_str_enumerate_lines): hint to suppress a
  maybe-uninitialized warning by gcc.

* thread.c (rb_fd_no_init): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57618 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

string.c

@@ -7517,6 +7517,9 @@ rb_str_enumerate_lines(int argc, VALUE *argv, VALUE str, int wantarray)
 	    wantarray = 0;
 #endif
 	}
+#if defined __GNUC__ && !defined __clang__
+	ASSUME(wantarray || !ary); /* if wantarray, ary does not matter */
+#endif
     }
     else {
 	if (wantarray)

thread.c

@@ -3573,8 +3573,8 @@ rb_fd_select(int n, rb_fdset_t *readfds, rb_fdset_t *writefds, rb_fdset_t *excep
     return select(n, r, w, e, timeout);
 }
 
-#if defined __GNUC__ && __GNUC__ >= 6
-#define rb_fd_no_init(fds) ASSUME(!(fds)->maxfd)
+#if defined __GNUC__ && __GNUC__ >= 4
+# define rb_fd_no_init(fds) ASSUME(!(fds)->fdset && !(fds)->maxfd)
 #endif
 
 #undef FD_ZERO
@@ -3640,6 +3640,10 @@ rb_fd_set(int fd, rb_fdset_t *set)
 #define FD_CLR(i, f)	rb_fd_clr((i), (f))
 #define FD_ISSET(i, f)	rb_fd_isset((i), (f))
 
+#if defined __GNUC__ && __GNUC__ >= 4
+# define rb_fd_no_init(fds) ASSUME(!(fds)->fdset)
+#endif
+
 #endif
 
 #ifndef rb_fd_no_init
@@ -3673,8 +3677,8 @@ update_timeval(struct timeval *timeout, double limit)
 }
 
 static int
-do_select(int n, rb_fdset_t *readfds, rb_fdset_t *writefds,
-	  rb_fdset_t *exceptfds, struct timeval *timeout)
+do_select(int n, rb_fdset_t *const readfds, rb_fdset_t *const writefds,
+	  rb_fdset_t *const exceptfds, struct timeval *timeout)
 {
     int MAYBE_UNUSED(result);
     int lerrno;