Merged PR 692379: Make DeveloperGuide more generic for VS version updates

Make DeveloperGuide more generic for VS version updates
Resolves Github issue #1313

Author: mpysson

Documentation/Wiki/DeveloperGuide.md

@@ -1,9 +1,13 @@
+# Overview
+There are two variants of BuildXL development: Public (default) and Internal (for Microsoft internal developers). The difference comes down to a few dependencies which are only availably internally within Microsoft today, like the connections to an internal cache server. The aquisition path for machine prerequesites may also differ slightly. 
+
+If you are a Microsoft internal developer, the Internal variant is automatically selected based on your user domain on Windows. On Linux and macOS you need to specify --internal in bxl.sh.
+
 # Prerequesites
 ## Windows
 * Windows 10 is the minimum requirement for BuildXL. You do not need to install [Visual Studio](https://visualstudio.microsoft.com/vs/) to get a working build, but it can be very helpful and is recommended for Windows development.
 * You will also need to install the Windows development kit. When you build the repo, the build script will determine if you have a compatible version installed and provide an error message with a link if one needs to be installed
-* [Visual Studio 2019 Build Tools](https://visualstudio.microsoft.com/downloads/) build tools must be installed. Scroll down to the "Tools for Visual Studio 2019" section, download and run the installer for "Build Tools for Visual Studio 2019". Within the Visual Studio installer under "Individual Components", search for and install "MSVC (v142) - VS 2019 C++ x64/x86 Spectre-mitigated libs (v14.29-16.10)".
-
+* (For the Public build) [Visual Studio 2019 Build Tools](https://visualstudio.microsoft.com/vs/older-downloads/#visual-studio-2019-and-other-products) build tools must be installed. Scroll down to the "Build Tools for Visual Studio" section, download and run the installer. Within the Visual Studio installer under "Individual Components", search for and install "MSVC (v142) - VS 2019 C++ x64/x86 Spectre-mitigated libs  (v14.28-16.8)". If you get an error about the build tools not being found after this installation, try setting the MSVC_VERSION environment variable to the exact version that was installed under "%Programfiles(x86)%\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC". See [visualCpp.dsc](../../Public/Sdk/Experimental/Msvc/VisualCpp/visualCpp.dsc) for more details about how this path is resolved
 
 ## Linux
 See [Prepare Linux VM](/Documentation/Wiki/LinuxDevelopment/How_to_prep_VM.md)

Public/Sdk/Experimental/Msvc/VisualCpp/visualCpp.dsc

@@ -88,7 +88,7 @@ function getMsvcPackage() : StaticDirectory {
     }
     else {
         let msvcVersions = [
-            "14.29.30037"
+            "14.28.29333"
         ];
 
         // ADO will set this variable if the version above is not installed