configure.ac: Default to --without-c-locale-coercion on Windows

--with-c-locale-coercion otherwise defaults to yes and enables code
that isn't compatible on Windows, mainly because the feature is Unix related.

Default to "no" on Windows instead.

Fixes python#36

configure.ac

@@ -4980,11 +4980,14 @@ AC_MSG_RESULT([$with_freelists])
 AC_MSG_CHECKING([for --with-c-locale-coercion])
 AC_ARG_WITH(
   [c-locale-coercion],
-  [AS_HELP_STRING([--with-c-locale-coercion], [enable C locale coercion to a UTF-8 based locale (default is yes)])])
+  [AS_HELP_STRING([--with-c-locale-coercion], [enable C locale coercion to a UTF-8 based locale (default is yes on Unix, no on Windows)])])
 
 if test -z "$with_c_locale_coercion"
 then
-    with_c_locale_coercion="yes"
+    case $host in
+      *-*-mingw*) with_c_locale_coercion="no";;
+      *) with_c_locale_coercion="yes";;
+    esac
 fi
 if test "$with_c_locale_coercion" != "no"
 then