Merge pull request zeromq#1810 from opedroso/IMPROVE_WINDOWS_BUILD

Problem:  Windows build script requires edit for DevStudio version

AUTHORS

@@ -111,6 +111,7 @@ Hardeep Singh
 André Caron 
 Tim Mossbarger 
 Doron Somech
+Osiris Pedroso
 
 Credits
 =======

INSTALL

@@ -14,6 +14,11 @@ If you clone the Git repository then you should start by running the
 command `./autogen.sh`. This is not necessary if you get the source
 packages.
 
+Windows Builds
+==============
+
+For Windows building, see the libzmq\builds\msvc\readme.txt file.
+
 Basic Installation
 ==================
 

builds/msvc/build/buildall.bat

@@ -1,12 +1,23 @@
 @ECHO OFF
+@setlocal
+::
+:: uses the environment from the DevStudio CMD window to figure out which version to build
+::
 
-CALL buildbase.bat ..\vs2015\libzmq.sln 14
-ECHO.
+set VSVER=%VSINSTALLDIR:~-5,2%
+set DIRVER=%VSVER%
+if %VSVER% gtr 10 set /a DIRVER = DIRVER + 1
+
+CALL buildbase.bat ..\vs20%DIRVER%\libzmq.sln %VSVER%
+
+:- CALL buildbase.bat ..\vs2015\libzmq.sln 14
+:- ECHO.
 :- CALL buildbase.bat ..\vs2013\libzmq.sln 12
 :- ECHO.
 :- CALL buildbase.bat ..\vs2012\libzmq.sln 11
 :- ECHO.
 :- CALL buildbase.bat ..\vs2010\libzmq.sln 10
 :- ECHO.
 
+@endlocal
 PAUSE

builds/msvc/readme.txt

@@ -13,3 +13,12 @@ The vs2015/vs2013/vs2012/vs2010 solution and project files differ only in versio
 More info here:
 
 http://en.wikipedia.org/wiki/Visual_C%2B%2B
+
+
+For building Windows, use the buildall.bat script in this directory.
+
+It requires that the CMD.EXE be created using the DevStudio Tools link to create a CMD.EXE windo.
+
+If multiple DevStudio versions are installed on the machine, you can run buildall.bat on separate windows that each were created by the desired DevStudio target.
+
+If you prefer to build all versions (or several) at the same time, you should uncomment the specific version desired in buildall.bat to build them from a single window.