gdk-pixbuf 2.38.1 release.

• Fix OOM in JPEG2000 loader [Ivan A. Melnikov, #107]
• Fix thumbnailing of animated GIFs [Debarshi Ray, #99]
• Multiple improvements to the GIF loader [Robert Ancell, !24, !28, !30, #22, #69
• Fix build on Windows/MSYS2 [Christoph Reiter, !29]
• Fix soname versioning on macOS [Christoph Reiter, !23]
• Cross-compilation fixes for Android [Matthew Waters, #64]
• Fix building modules on macOS [Ignacio Casal Quinteiro, !18 and !19]
• Fix introspection generation [Iain Lane, #92]
• Fix error handling in PNG loader [Debarshi Ray, !16]
• Improve reproducibility of the build [Chris Lamb, !15]
• Speed up saving PNG files [Brion Vibber, #90]
• Add variables in the pkg-config files for binary utilities [Emmanuele Bassi, #88]
• Build fixes [Emmanuele Bassi, #88]