[m-rev.] for post-commit review: document 64-bit MSVC support

[Julien Fischer]

For post-commit review by anyone.

I'll update the NEWS file separately.

-----------------------------------

Document 64-bit MSVC support.

README.MS-VisualC.md:
     Document how to use the 64-bit version of MSVC. Delete references
     to the 64-bit version not being supported.

Julien.

diff --git a/README.MS-VisualC.md b/README.MS-VisualC.md
index 3efc5a5..8a08488 100644
--- a/README.MS-VisualC.md
+++ b/README.MS-VisualC.md
@@ -3,7 +3,9 @@ Mercury with Microsoft Visual C++

  Mercury has been ported to use the Microsoft Visual C++ compiler (MSVC).
  It requires at least version 12.0 (2013); older versions lack sufficient C99
-support.
+support. Version 19.0 (2022) is recommended when using the 64-bit (x64) version
+of MSVC. Support for 64-bit code and MSVC has *not* been tested with older
+versions.

  Setting up the build environment
  --------------------------------
@@ -24,18 +26,35 @@ shells do the following:

           Start -> Visual Studio YYYY -> Visual Studio Tools

-    although the name and location vary between different versions and editions
-    of Visual Studio.  (*YYYY* is the year.)
+   although the name and location vary between different versions and editions
+   of Visual Studio. (*YYYY* is the year.) Note that this will give you the
+   x86 version of MSVC.
+
+   The Visual Studio entry in the `Start` menu may also have items named
+   similarly to:
+
+        * x64 Native Tools Command Prompt for VS 2022
+        * x86 Native Tools Command Prompt for VS 2022
+
+   These allow you to select between the x64 and x86 versions of MSVC toolchain.
+
+   Alternatively, you can start a `cmd.exe` session and use the batch files supplied
+   with Visual Studio (e.g. `vcvarsall.bat`, `vcvars32.bat` or `vcvars64.bat`) to
+   set up the environment for MSVC.

  2. Enter the following command to start the MSYS shell:

          C:\> C:\MinGW\MSYS\1.0\msys.bat

-    or this one to start the MSYS2 shell:
+   or this one to start the MSYS2 shell with 32-bit MSVC:

          C:\> C:\msys64\msys2_shell.cmd -use-full-path -mingw32

-    or this one to start the Cygwin shell:
+   or this one ot start the MSYS2 shell with 64-bit MSVC:
+ 
+        C:\> C:\msys64\msys2_shell.cmd -use-full-path -mingw64
+
+   or this one to start the Cygwin shell:

          C:\> C:\CYGWIN\cygwin.bat

@@ -46,15 +65,11 @@ returned by autoconf match `*mingw*`; in particular it must *not* match
  `*-pc-msys`. You can use the `config.guess` script to see what configuration
  type autoconf detects.

-In order to install the C# or Java grades you will require a C# or Java
-compiler to be included in the Windows `PATH`.
+To install the C# or Java grades you will require a C# or Java compiler to be
+included in the Windows `PATH`.
  (See the relevant README files for further details, e.g.
  [README.Java.md](README.Java.md) etc)

-Note that `boehm_gc/NT_MAKEFILE` supports both i386 and x64 architectures,
-but the MSVC port can only target i386 for now. The architecture is controlled
-by the CPU parameter of `NT_MAKEFILE`.
-
  Configuration and Installation
  ------------------------------

@@ -135,10 +150,6 @@ The MSVC port currently has a number of limitations:
    This is due to it containing a number of Unix dependencies. (Other
    tools that work with deep profiles should be fine.)

-* Generation of 64-bit code using Mercury and MSVC is not yet supported.
-  To generate native 64-bit executables on Windows you will need to use
-  the MinGW64 port (see README.MinGW for details).
-
  * When used directly from the Windows command prompt, mmake will not work.
    You should use `mmc --make` instead. (`mmake` requires a POSIX-like shell
    and GNU `make`; it will however work with the Cygwin or MSYS shells.)