Include <wchar.h> for towlower, towupper, to avoid implicit function
declarations and build failures with future compilers.

Submitted upstream: <https://sourceforge.net/p/dc3dd/bugs/22/>

diff --git a/configure b/configure
index 1901a37..5a4b0c3
--- a/configure
+++ b/configure
@@ -54147,6 +54147,7 @@ cat >>conftest.$ac_ext <<_ACEOF
 #endif
 #include <stdlib.h>
 #include <string.h>
+#include <wctype.h>
 struct tm t;
 char buf[16];
 int main () {
@@ -54913,6 +54914,7 @@ cat >>conftest.$ac_ext <<_ACEOF
 #endif
 #include <stdlib.h>
 #include <string.h>
+#include <wctype.h>
 struct tm t;
 char buf[16];
 int main () {
diff --git a/m4/locale-tr.m4 b/m4/locale-tr.m4
index d6a2088..d92c674 100644
--- a/m4/locale-tr.m4
+++ b/m4/locale-tr.m4
@@ -20,6 +20,7 @@ changequote(,)dnl
 #endif
 #include <stdlib.h>
 #include <string.h>
+#include <wctype.h>
 struct tm t;
 char buf[16];
 int main () {