build: add MSVS 2015 support

This is a port of 4208dc4 .

Original commit message:

  PR-URL: #2036
  Reviewed-By: Alexis Campailla <alexis@janeasystems.com>

This was ported to v0.10 in nodejs/node-v0.x-archive#25857

PR-URL: #2843
Reviewed-By: rvagg - Rod Vagg <rod@vagg.org>
Reviewed-By: orangemocha - Alexis Campailla <orangemocha@nodejs.org>
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>

vcbuild.bat

@@ -108,6 +108,29 @@ if defined NIGHTLY set TAG=nightly-%NIGHTLY%
 
 @rem Set environment for msbuild
 
+@rem Look for Visual Studio 2015
+echo Looking for Visual Studio 2015
+if not defined VS140COMNTOOLS goto vc-set-2013
+if not exist "%VS140COMNTOOLS%\..\..\vc\vcvarsall.bat" goto vc-set-2013
+echo Found Visual Studio 2015
+if defined msi (
+  echo Looking for WiX installation for Visual Studio 2015...
+  if not exist "%WIX%\SDK\VS2015" (
+    echo Failed to find WiX install for Visual Studio 2015
+    echo VS2015 support for WiX is only present starting at version 3.10
+    goto vc-set-2013
+  )
+)
+if "%VCVARS_VER%" NEQ "140" (
+  call "%VS140COMNTOOLS%\..\..\vc\vcvarsall.bat"
+  SET VCVARS_VER=140
+)
+if not defined VCINSTALLDIR goto msbuild-not-found
+set GYP_MSVS_VERSION=2015
+set PLATFORM_TOOLSET=v140
+goto msbuild-found
+
+:vc-set-2013
 @rem Look for Visual Studio 2013
 echo Looking for Visual Studio 2013
 if not defined VS120COMNTOOLS goto vc-set-2012
@@ -117,6 +140,7 @@ if defined msi (
   echo Looking for WiX installation for Visual Studio 2013...
   if not exist "%WIX%\SDK\VS2013" (
     echo Failed to find WiX install for Visual Studio 2013
+    echo VS2013 support for WiX is only present starting at version 3.8
     goto vc-set-2012
   )
 )