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, 4 insertions, 4 deletions

diff --git a/src/xterm.c b/src/xterm.c
index e9068830f85..c8836b7ca78 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -2005,9 +2005,9 @@ x_draw_glyphless_glyph_string_foreground (struct glyph_string *s)
         }
       else if (glyph->u.glyphless.method == GLYPHLESS_DISPLAY_HEX_CODE)
         {
-          sprintf (buf, "%0*X",
-                   glyph->u.glyphless.ch < 0x10000 ? 4 : 6,
-                   glyph->u.glyphless.ch + 0u);
+          unsigned int ch = glyph->u.glyphless.ch;
+          eassume (ch <= MAX_CHAR);
+          sprintf (buf, "%0*X", ch < 0x10000 ? 4 : 6, ch);
           str = buf;
         }
 
@@ -8949,7 +8949,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
         {
         case MappingModifier:
           x_find_modifier_meanings (dpyinfo);
-          /* This is meant to fall through.  */
+          FALLTHROUGH;
         case MappingKeyboard:
           XRefreshKeyboardMapping ((XMappingEvent *) &event->xmapping);
         }