Give pwd -W a try

CI/before_script.msvc.sh

@@ -419,8 +419,9 @@ fi
 			printf "Exists. "
 		elif [ -z $SKIP_EXTRACT ]; then
 			rm -rf Boost
-			"${DEPS}/boost-1.67.0-msvc${MSVC_YEAR}-win${BITS}.exe" //DIR="${TMP}\boost" //VERYSILENT //NORESTART //SUPPRESSMSGBOXES //LOG="boost_install.log"			
+			REAL_TEMP_PATH=`cd ${TMP} && pwd -W`
-			mv "%TMP%\boost" ${BOOST_SDK}
+			"${DEPS}/boost-1.67.0-msvc${MSVC_YEAR}-win${BITS}.exe" //DIR="${REAL_TEMP_PATH}\boost" //VERYSILENT //NORESTART //SUPPRESSMSGBOXES //LOG="boost_install.log"			
+			mv "${REAL_TEMP_PATH}\boost" ${BOOST_SDK}
 		fi
 
 		add_cmake_opts -DBOOST_ROOT="$BOOST_SDK" \