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, 1 deletions

diff --git a/src/data.c b/src/data.c
index 44f7ba0e881..3ff2a809744 100644
--- a/src/data.c
+++ b/src/data.c
@@ -2153,7 +2153,7 @@ If the current binding is global (the default), the value is nil.  */)
         else if (!BUFFER_OBJFWDP (valcontents))
           return Qnil;
       }
-      /* FALLTHROUGH */
+      FALLTHROUGH;
     case SYMBOL_LOCALIZED:
       /* For a local variable, record both the symbol and which
          buffer's or frame's value we are saving.  */