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/doprnt.c b/src/doprnt.c
index 09051adc053..bed9350f4a6 100644
--- a/src/doprnt.c
+++ b/src/doprnt.c
@@ -352,6 +352,7 @@ doprnt (char *buffer, ptrdiff_t bufsize, const char *format,
 
 	    case 'S':
 	      string[-1] = 's';
+	      FALLTHROUGH;
 	    case 's':
 	      if (fmtcpy[1] != 's')
 		minlen = atoi (&fmtcpy[1]);