A simpler wrapper for vcvarsall.bat which only does the work on the first run

vcvarsall.bat

@echo off

:: Path to vcvarsall.bat from Visual Studio
:: When called, it makes cl.exe (C++ compiler) and link.exe (Linker) available in PATH.
set VCVARSPATH="C:\Program Files (x86)\Microsoft Visual Studio\VC\Auxiliary\Build\vcvarsall.bat"

if "%VSISSET%"=="" (
        %VCVARSPATH% %*
        if "%ERRORLEVEL%"=="0" (
                set VSISSET=%*
        ) else (
                echo [vcvars returned %ERRORLEVEL%; resetting]
        )
) else (
        echo [skipping vcvarsall; already set]
)