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, 3 insertions, 1 deletions

diff --git a/src/ccl.c b/src/ccl.c
index 90bd2f46794..b2caf413f7a 100644
--- a/src/ccl.c
+++ b/src/ccl.c
@@ -1000,7 +1000,7 @@ ccl_driver (struct ccl_program *ccl, int *source, int *destination, int src_size
 
         case CCL_ReadBranch:    /* CCCCCCCCCCCCCCCCCCCCrrrXXXXX */
           CCL_READ_CHAR (reg[rrr]);
-          /* fall through ... */
+          FALLTHROUGH;
         case CCL_Branch:        /* CCCCCCCCCCCCCCCCCCCCrrrXXXXX */
         {
           int ioff = 0 <= reg[rrr] && reg[rrr] < field1 ? reg[rrr] : field1;
@@ -1174,6 +1174,7 @@ ccl_driver (struct ccl_program *ccl, int *source, int *destination, int src_size
 
         case CCL_ReadJumpCondExprConst: /* A--D--D--R--E--S--S-rrrXXXXX */
           CCL_READ_CHAR (reg[rrr]);
+          FALLTHROUGH;
         case CCL_JumpCondExprConst: /* A--D--D--R--E--S--S-rrrXXXXX */
           i = reg[rrr];
           jump_address = ic + ADDR;
@@ -1184,6 +1185,7 @@ ccl_driver (struct ccl_program *ccl, int *source, int *destination, int src_size
 
         case CCL_ReadJumpCondExprReg: /* A--D--D--R--E--S--S-rrrXXXXX */
           CCL_READ_CHAR (reg[rrr]);
+          FALLTHROUGH;
         case CCL_JumpCondExprReg:
           i = reg[rrr];
           jump_address = ic + ADDR;