Add escaping to allow spaces in ${CMAKE_CURRENT_BINARY_DIR}

The build was failing due to spaces in the username appearing in ${CMAKE_CURRENT_BINARY_DIR}:

FAILED: share/templates/CMakeFiles/inkscape_default_svg
cmd.exe /C "cd /D "C:\msys64\home\Tim Rawlinson\master\share\templates" && sh -c "C:/msys64/home/Tim Rawlinson/master/share/templates/create_defaults.pl" && sh -c "mv default-* C:/msys64/home/Tim Rawlinson/master/build/share/templates""
sh: C:/msys64/home/Tim: No such file or directory

This merge adds appropriate quotation marks and escaping to fix the issue.