Update to reflect use of vc14x binary in place of vc14[012]

Closes https://github.com/wxWidgets/wxWidgets/pull/1608

docs/contributing/how-to-release.md

@@ -157,7 +157,7 @@ in the generated files too.
 
 To build official x86 and x64 shared binaries the following are prerequisites:
 
-     - Visual Studio 2008, 2010, 2012, 2013, 2015, 2017, 2019
+     - Visual Studio 2008, 2010, 2012, 2013 and 2015
      - Windows SDK 6.1, 7.1 (required for x64 builds for Visual Studio 2008, 2010)
      - 7z (required for packaging the files)
      - fciv (required for generating the checksums)
@@ -172,15 +172,6 @@ WINDOWS71SDK
 
 If either of these are blank they are set to the default install location.
 
-For Visual Studio 2017 and 2019 the VSxxxxCOMNTOOLS environment variable is not
-set by the installer as these two versions support multiple toolsets.
-The build script will check the following in sequence:
- - If VSxxxCOMNTOOLS is set (xxx=141: VS2017, xxx=142: VS2019) it is used as
-   the path to call VsDevCmd.bat to set up the environmet.
- - If VSxxxCOMNTOOLS is not set, then the Visual Studio tool vswhere is used
-   to find the latest installed toolset for the compiler and the associated
-   VsDevCmd.bat file is used to set up the environment.
-
 To build binaries for a single compiler, open a command prompt (for Visual
 Studio 2008 only an SDK 6.1 developer's command prompt must be used),
 cd to the build\tools\msvs folder and run the batch file 'officialbuild'
@@ -190,9 +181,10 @@ with the vcXXX version number:
     Visual Studio 2010  vc100
     Visual Studio 2012  vc110
     Visual Studio 2014  vc120
-    Visual Studio 2015  vc140
-    Visual Studio 2017  vc141
-    Visual Studio 2019  vc142
+    Visual Studio 2015  vc14x
+
+The Visual Studio 2015, 2017 and 2019 are binary compatible, allowing the
+vc14x binary to be used with any of them.
 
 This will build all of the x86 and x64 binaries for the selected compiler version,
 package them in 7z files and calculate the checksums. The 7z files and the