Encoding: Switch to use UTF-8 internally by default on Windows.

This fixes several reported bugs about CMake not handling
non-ascii paths on Windows.

Practically, the use of some unicode characters may still
be limited by the build or compiler tools.

For example, a user may be limited by the build tools to
using characters within the Windows ANSI code page (which can
include non-ascii characters in the current system language).

Help/release/dev/windows-utf-8.rst

@@ -0,0 +1,22 @@
+windows-utf-8
+-------------
+
+* On Windows, CMake learned to support international characters.
+  This allows use of characters from multiple (spoken) languages
+  in CMake code, paths to source files, configured files such as
+  ``.h.in`` files, and other files read and written by CMake.
+  Because CMake interoperates with many other tools, there may
+  still be some limitations when using certain international
+  characters.
+
+  Files written in the :manual:`cmake-language(7)`, such as
+  ``CMakeLists.txt`` or ``*.cmake`` files, are expected to be
+  encoded as UTF-8.  If files are already ASCII, they will be
+  compatible.  If files were in a different encoding, including
+  Latin 1, they will need to be converted.
+
+  The Visual Studio generators now write solution and project
+  files in UTF-8 instead of Windows-1252.  Windows-1252 supported
+  Latin 1 languages such as those found in North and South America
+  and Western Europe.  With UTF-8, additional languages are now
+  supported.