anchor.diff:  @echo.
   @md cmake-%abi%
   @cd cmake-%abi%
  -@call "%vsenv%"
  +@call %vsenv%
   @set vsenvloaded=1
   @if %abi%==x64 @set toolchain=%toolchain% Win64
   @set PATH=%mesa%cmake\%abi%\bin\;%PATH%
  
positive.code: @del requirements.txt
  @echo.
  @if %vsenvloaded%==0 (
  @call "%vsenv%"
  @echo.
  )
  
  
negative.code: @if %abi%==x64 @set altabi=%longabi%
  @set minabi=32
  @if %abi%==x64 set minabi=64
  @set vsenv="%ProgramFiles%
  @if NOT "%ProgramW6432%"=="" set vsenv=%vsenv% (x86)
  @set vsenv=%vsenv%\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars%minabi%.bat"
  @set toolchain=Visual Studio 15 2017
  @if NOT EXIST %vsenv% (
  @set vsenv="%VS140COMNTOOLS%..\..\VC\bin\vcvars%minabi%.bat"
  @set toolchain=Visual Studio 14
  )
  @set gcc=%mesa%mingw-w64-%abi%\mingw%minabi%\bin
  