Merge with gnulib, pacifying GCC 7

This incorporates:
2017-05-16 manywarnings: update for GCC 7
2017-05-15 sys_select: Avoid "was expanded before it was required"
* configure.ac (nw): Suppress GCC 7’s new -Wduplicated-branches and
-Wformat-overflow=2 options, due to too many false alarms.
* doc/misc/texinfo.tex, lib/strftime.c, m4/manywarnings.m4:
Copy from gnulib.
* m4/gnulib-comp.m4: Regenerate.
* src/coding.c (decode_coding_iso_2022):
Fix bug uncovered by -Wimplicit-fallthrough.
* src/conf_post.h (FALLTHROUGH): New macro.
Use it to mark all switch cases that fall through.
* src/editfns.c (styled_format): Use !, not ~, on bool.
* src/gtkutil.c (xg_check_special_colors):
When using sprintf, don’t trust Gtk to output colors in [0, 1] range.
(xg_update_scrollbar_pos): Avoid use of possibly-uninitialized bool;
this bug was actually caught by Clang.
* src/search.c (boyer_moore):
Tell GCC that CHAR_BASE, if nonzero, must be a non-ASCII character.
* src/xterm.c (x_draw_glyphless_glyph_string_foreground):
Tell GCC that glyph->u.glyphless.ch must be a character.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/callint.c b/src/callint.c
index d96454883cf..96436116c8b 100644
--- a/src/callint.c
+++ b/src/callint.c
@@ -690,6 +690,7 @@ invoke it.  If KEYS is omitted or nil, the return value of
 	case 'N':     /* Prefix arg as number, else number from minibuffer.  */
 	  if (!NILP (prefix_arg))
 	    goto have_prefix_arg;
+	  FALLTHROUGH;
 	case 'n':		/* Read number from minibuffer.  */
 	  args[i] = call1 (Qread_number, callint_message);
 	  /* Passing args[i] directly stimulates compiler bug.  */