Log Message:
librsvg: update to 2.40.20.

Version 2.40.20
- Except for emergencies, this will be the LAST RELEASE of the
  librsvg-2.40.x series.  We are moving to 2.41, which is vastly
  improved over the 2.40 series.  The API/ABI there remain unchaged,
  so we strongly encourage you to upgrade your sources and binaries to
  librsvg-2.41.x.
- bgo#761175 - Allow masks and clips to reuse a node being drawn.
- Don't access the file system when deciding whether to load a remote
  file with a UNC path for a paint server (i.e. don't try to load it at all).
- Vistual Studio: fixed and integrated introspection builds, so
  introspection data is built directly from the Visual Studio project
  (Chun-wei Fan).
- Visual Studio: We now use HIGHENTROPYVA linker option on x64 builds,
  to enhance the security of built binaries (Chun-wei Fan).
- Fix generation of Vala bindings when compiling in read-only source
  directories (Emmanuele Bassi).