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, 5 insertions, 3 deletions

diff --git a/src/syntax.c b/src/syntax.c
index 7aa43e6e5c7..dcaca22f0e2 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -810,6 +810,7 @@ back_comment (ptrdiff_t from, ptrdiff_t from_byte, ptrdiff_t stop,
 	case Sstring_fence:
 	case Scomment_fence:
 	  c = (code == Sstring_fence ? ST_STRING_STYLE : ST_COMMENT_STYLE);
+	  FALLTHROUGH;
 	case Sstring:
 	  /* Track parity of quotes.  */
 	  if (string_style == -1)
@@ -2690,6 +2691,7 @@ scan_lists (EMACS_INT from, EMACS_INT count, EMACS_INT depth, bool sexpflag)
 		goto lose;
 	      INC_BOTH (from, from_byte);
 	      /* Treat following character as a word constituent.  */
+	      FALLTHROUGH;
 	    case Sword:
 	    case Ssymbol:
 	      if (depth || !sexpflag) break;
@@ -2721,7 +2723,7 @@ scan_lists (EMACS_INT from, EMACS_INT count, EMACS_INT depth, bool sexpflag)
 
 	    case Scomment_fence:
 	      comstyle = ST_COMMENT_STYLE;
-	      /* FALLTHROUGH */
+	      FALLTHROUGH;
 	    case Scomment:
 	      if (!parse_sexp_ignore_comments) break;
 	      UPDATE_SYNTAX_TABLE_FORWARD (from);
@@ -2753,7 +2755,7 @@ scan_lists (EMACS_INT from, EMACS_INT count, EMACS_INT depth, bool sexpflag)
 		  goto close1;
 		}
 	      mathexit = 1;
-
+	      FALLTHROUGH;
 	    case Sopen:
 	      if (!++depth) goto done;
 	      break;
@@ -2909,7 +2911,7 @@ scan_lists (EMACS_INT from, EMACS_INT count, EMACS_INT depth, bool sexpflag)
 		  goto open2;
 		}
 	      mathexit = 1;
-
+	      FALLTHROUGH;
 	    case Sclose:
 	      if (!++depth) goto done2;
 	      break;