Add progress output to build script in SCons

[qustrolabe]

Trying to build Godot with SCons build system I noticed that there are no output of compiling progress (like percentage or something like "build 563 files out of 5000"), quickly checking SConstruct found that there are "progress" flag (which is unexpectedly already set to True), and there are function called show_progress methods.py.

Investigating this function I found that there dictionary node_count_data, changing "max" value to for example 10000 result in SCons successfully printing percentage of built files.

node_count_data = {
  "count": 0,
  "max": 0,
  "interval": 1,
  "fname": str(env.Dir("#")) + "/.scons_node_count",
}

However I can't find any code that changes "max" value for me before build. But I found that there are function "progress_finish" which saves node_count and maybe it is called right after engine were built to make progress percentage work only after whole project was built to show percentage to anyone who is rebuilding project after small changes.

That's why I'm suggesting to add proper progress output, at least something similar to CMake's one, there's no serious need in it, but it will be useful for anyone new to SCons to understand whether you started new build or continued previous one (I've got return-type error and tried to play with building flags and apparently started build from start).