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/regex.c b/src/regex.c
index 8e38a920cdb..ed848902086 100644
--- a/src/regex.c
+++ b/src/regex.c
@@ -2636,6 +2636,7 @@ regex_compile (const_re_char *pattern, size_t size,
           if ((syntax & RE_BK_PLUS_QM)
               || (syntax & RE_LIMITED_OPS))
             goto normal_char;
+          FALLTHROUGH;
         handle_plus:
         case '*':
           /* If there is no previous pattern...  */
@@ -3086,6 +3087,7 @@ regex_compile (const_re_char *pattern, size_t size,
                                    with non-0. */
                                 if (regnum == 0)
                                   FREE_STACK_RETURN (REG_BADPAT);
+                                FALLTHROUGH;
                               case '1': case '2': case '3': case '4':
                               case '5': case '6': case '7': case '8': case '9':
                                 regnum = 10*regnum + (c - '0'); break;
@@ -3905,8 +3907,7 @@ analyze_first (const_re_char *p, const_re_char *pend, char *fastmap,
                  j < (1 << BYTEWIDTH); j++)
               fastmap[j] = 1;
           }
-
-          /* Fallthrough */
+          FALLTHROUGH;
         case charset:
           if (!fastmap) break;
           not = (re_opcode_t) *(p - 1) == charset_not;
@@ -6182,8 +6183,7 @@ re_match_2_internal (struct re_pattern_buffer *bufp, const_re_char *string1,
             case on_failure_jump_nastyloop:
               assert ((re_opcode_t)pat[-2] == no_op);
               PUSH_FAILURE_POINT (pat - 2, str);
-              /* Fallthrough */
-
+              FALLTHROUGH;
             case on_failure_jump_loop:
             case on_failure_jump:
             case succeed_n: