so that godot package builds reproducibly
in spite of indeterministic filesystem readdir order
and http://bugs.python.org/issue30461

See https://reproducible-builds.org/ for why this is good.

Sort font input file list, so that builtin_fonts.gen.h
is created in a reproducible way

Sort list of platforms, so that editor/register_exporters.gen.cpp
is created in a reproducible way

Sort list of source files, so that .a files and resulting godot binaries
are created in a reproducible way