Remove test for, and fallback impl of, wmemchr.

This was introduced in commit e7acb9f696, as a side effect of
also wanting to call wmemchr to find a NUL wide character in the
buffer returned from GetDlgItemTextW. But the previous commit has
superseded that code, so now we don't use wmemchr in this code base
any more. Remove the machinery that provides it, saving a now-useless
cmake configure-time check.

cmake/cmake.h.in

@@ -15,7 +15,6 @@
 #cmakedefine01 HAVE_GETNAMEDPIPECLIENTPROCESSID
 #cmakedefine01 HAVE_SETDEFAULTDLLDIRECTORIES
 #cmakedefine01 HAVE_STRTOUMAX
-#cmakedefine01 HAVE_WMEMCHR
 #cmakedefine01 HAVE_DWMAPI_H
 
 #cmakedefine NOT_X_WINDOWS

cmake/platforms/windows.cmake

@@ -53,7 +53,6 @@ define_negation(NO_HTMLHELP HAVE_HTMLHELP_H)
 check_include_files("winsock2.h;afunix.h" HAVE_AFUNIX_H)
 
 check_symbol_exists(strtoumax "inttypes.h" HAVE_STRTOUMAX)
-check_symbol_exists(wmemchr "wchar.h" HAVE_WMEMCHR)
 check_symbol_exists(AddDllDirectory "windows.h" HAVE_ADDDLLDIRECTORY)
 check_symbol_exists(SetDefaultDllDirectories "windows.h"
   HAVE_SETDEFAULTDLLDIRECTORIES)

defs.h

@@ -53,11 +53,6 @@ uintmax_t strtoumax(const char *nptr, char **endptr, int base);
 #define SIZEu "zu"
 #endif
 
-#if !HAVE_WMEMCHR
-/* Work around lack of wmemchr in older MSVC */
-wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
-#endif
-
 #if defined __GNUC__ || defined __clang__
 /*
  * On MinGW, the correct compiler format checking for vsnprintf() etc

windows/CMakeLists.txt

@@ -42,9 +42,6 @@ add_sources_from_current_dir(utils
 if(NOT HAVE_STRTOUMAX)
   add_sources_from_current_dir(utils utils/strtoumax.c)
 endif()
-if(NOT HAVE_WMEMCHR)
-  add_sources_from_current_dir(utils utils/wmemchr.c)
-endif()
 add_sources_from_current_dir(eventloop
   cliloop.c handle-wait.c)
 add_sources_from_current_dir(console

windows/utils/wmemchr.c

@@ -1,15 +0,0 @@
-/*
- * Work around lack of wmemchr in older MSVC libraries.
- */
-
-#include <wchar.h>
-
-#include "defs.h"
-
-wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n)
-{
-    for (; n != 0; s++, n--)
-        if (*s == c)
-            return (wchar_t *)s;
-    return NULL;
-}