Updated the building instructions in BUILDING.md.

BUILDING.md

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+## Building VARCem from Source
+
+
+#### Fred N. van Kempen, <decwiz@yahoo.com>
+
+#### Last Updated: 03/26/2018
+
+
+These instructions guide you in building the **VARCem** emulator from
+its published sources. Currently, the emulator can be built for **Windows**,
+**Linux** (Debian-tested) and **BSD UNIX** (FreeBSD-tested). More supported 
+platforms will be added as time permits.
+
+
+#### Microsoft Windows
+
+#### Get the sources.
+Get a copy of the source tree (by cloning the GIT repository, or
+by downloading a ZIP archive from GIT, or from the website) and
+unpack (if needed) them into a folder:
+
+  `D:`
+  
+  `cd \VARCem`
+  
+  `mkdir src`
+  
+  `cd src`
+  
+  `unzip varcem-0.1.3.zip`
+
+which puts the source tree into the *D:\VARCem\src* folder.
+
+For the Windows environment, two methods of compiling these sources are currently possible:
+
+##### Using Microsoft's Visual Studio development system.
+Tested with versions **2015** ("VC14") and **2017*** ("VC15"), this is now a
+fairly easy process.
+
+1.  Install the Visual Studio system (the *Community* release is sufficient) and make sure it works.
+
+2.  Go to the *win\msvc* folder, then to the *vc14* folder for Visual Studio 2015, or to the *vc15* folder for the 2017 release of Visual Studio.
+
+3.  Double-click on the *VARCem.sln* solution file, and Visual Studio will load the project for you.
+
+4.  Select your preferred type of build (x86 or x64, Debug or Release) and build the project.
+
+**All done!**  You can repeat this for other build types if so desired.
+
+For those who prefer to use **command-line tools** to process a *Makefile* (the author is such an oddity), you can also open up a **Visual Studio Command Prompt** from the Start Menu, and type the command:
+
+  `d:`
+
+  `cd \VARCem\src`
+
+  `make -f win\msvc\Makefile.VC`
+  
+and voila, there it goes. If things are set up properly, this is about the fastest way to compile the sources on Windows.
+
+##### Using the MSYS2 "MinGW" toolset.
+Building the emulator is also possible using the free **MinGW** compiler toolset, which is based on the well-known *gcc* toolset. Although also available as a standalone project, we will use the version that is part of the **MSYS2** project, which aims to create a *usable Linux-like environment on the Windows platform*. The MinGW toolset is part of that environment.
+
+1.  Download the most recent **MSYS2** distribution for your system.
+
+    Please note that MSYS2 is a *64-bit application*, even though it
+    (also) contains a 32-bit MinGW compiler.
+
+2.  Install MSYS2 onto your system, using either *C:\msysS2* or the
+    suggested *C:\msysS64* folders as a root folder.
+
+3.  The standard installation of MSYS2 does not include a compiler
+    or other 'build tools'. This is surprising, given the main
+    objecttive of the project, but so be it.
+
+    The easiest way to install packages like these is to use its
+    built-in package manager, **pacman**.  You can install a full
+    "base setup" for GCC and friends with the command:
+
+      `pacman -S --needed base-devel mingw-w64-i686-toolchain \`
+   
+      `mingw-w64-x86_64-toolchain git subversion mercurial \`
+      
+	  `mingw-w64-i686-cmake mingw-w64-x86_64-cmake`
+
+    (the backslashes are only for clarity; you can type it as one
+    single line if you wish.)
+
+    Pacman will show you the various packages and sub-packages to
+    install, just type **ENTER** to agree, followed by a **y** to begin
+    downloading and installing these packages.
+
+4.  Make sure this step worked, by typing commands like:
+
+     `cc`
+
+     `gcc`
+
+     `make`
+
+    just so we know this is done.
+
+5.  You may want to install a text editor of choice; in our case, we
+    will install the **vi** (or, really, **Vim**) editor, using the package
+    manager:
+
+      `pacman -S vim`
+
+    Again, make sure this step worked.
+
+6.  Finally, we are good to go at compiling the VARCem sources.
+
+    You are now ready to build, using a command like:
+
+      `make -f win/mingw/Makefile.MinGW`
+
+    which will hopefully build the application's executables.
+
+With these steps, you have set up a build environment, suitable
+to build (and develop !) the VARCem project application(s) for
+Windows.
+