enable PYARROW_WITH_S3 on appveyor

ci/cpp-msvc-build-main.bat

@@ -98,6 +98,9 @@ pip install -r requirements.txt pickle5
 
 set PYARROW_CXXFLAGS=%ARROW_CXXFLAGS%
 set PYARROW_CMAKE_GENERATOR=%GENERATOR%
+if "%ARROW_S3%" == "ON" (
+  set PYARROW_WITH_S3="ON"
+)
 if "%ARROW_BUILD_FLIGHT%" == "ON" (
   @rem ARROW-5441: bundling Arrow Flight libraries not implemented
   set PYARROW_BUNDLE_ARROW_CPP=OFF