BuildSystem: Sort input file lists

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

SConstruct

@@ -23,7 +23,7 @@ platform_exporters = []
 platform_apis = []
 global_defaults = []
 
-for x in glob.glob("platform/*"):
+for x in sorted(glob.glob("platform/*")):
     if (not os.path.isdir(x) or not os.path.exists(x + "/detect.py")):
         continue
     tmppath = "./" + x