message: Appveyor: add cmake build dir.
diff: @@ -28,6 +28,7 @@ before_build:
  - if exist "%QT5%" cmake -H. -Bbuild -G "%CMAKE_GENERATOR%" "-DCMAKE_PREFIX_PATH=%QT5%"
  build_script:
  +- md build
  - if "%APPVEYOR_REPO_TAG%"=="true" (set CONFIGURATION=RelWithDebInfo) else (set CONFIGURATION=Debug)
  - cmake --build build --config "%CONFIGURATION%" -- %MSBUILD_FLAGS%
  