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, 6 insertions, 4 deletions

diff --git a/src/lread.c b/src/lread.c
index c03aad4f722..5e737d690c6 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2309,6 +2309,7 @@ read_escape (Lisp_Object readcharfun, bool stringp)
       c = READCHAR;
       if (c != '-')
         error ("Invalid escape character syntax");
+      FALLTHROUGH;
     case '^':
       c = READCHAR;
       if (c == '\\')
@@ -2399,6 +2400,7 @@ read_escape (Lisp_Object readcharfun, bool stringp)
     case 'U':
       /* Post-Unicode-2.0: Up to eight hex chars.  */
       unicode_hex_count = 8;
+      FALLTHROUGH;
     case 'u':
 
       /* A Unicode escape.  We only permit them in strings and characters,
@@ -3278,11 +3280,11 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
             *pch = c;
             return Qnil;
           }
-
-        /* Otherwise, we fall through!  Note that the atom-reading loop
-           below will now loop at least once, assuring that we will not
-           try to UNREAD two characters in a row.  */
       }
+      /* The atom-reading loop below will now loop at least once,
+         assuring that we will not try to UNREAD two characters in a
+         row.  */
+      FALLTHROUGH;
     default:
     default_label:
       if (c <= 040) goto retry;