Declare setting object in settings.py (emscripten-core#13918)

Breaks at least one dependency cycle between cache.py and shared.py.

This is quite a big change but it roughly equates to renaming
`shared.Settings` to just `settings` in most location.  This makes use
of settings more concise and readable.

Author: sbc100

embuilder.py

@@ -19,6 +19,7 @@
 
 from tools import shared
 from tools import system_libs
+from tools.settings import settings
 import emscripten
 
 
@@ -106,9 +107,9 @@ def get_help():
 
 def build_port(port_name):
   if force:
-    system_libs.clear_port(port_name, shared.Settings)
+    system_libs.clear_port(port_name, settings)
 
-  system_libs.build_port(port_name, shared.Settings)
+  system_libs.build_port(port_name, settings)
 
 
 def main():
@@ -139,10 +140,10 @@ def main():
   shared.check_sanity()
 
   if args.lto:
-    shared.Settings.LTO = "full"
+    settings.LTO = "full"
 
   if args.pic:
-    shared.Settings.RELOCATABLE = 1
+    settings.RELOCATABLE = 1
 
   if args.force:
     force = True
@@ -187,9 +188,9 @@ def main():
     elif what == 'icu':
       build_port('icu')
     elif what == 'zlib':
-      shared.Settings.USE_ZLIB = 1
+      settings.USE_ZLIB = 1
       build_port('zlib')
-      shared.Settings.USE_ZLIB = 0
+      settings.USE_ZLIB = 0
     elif what == 'bzip2':
       build_port('bzip2')
     elif what == 'bullet':
@@ -207,56 +208,56 @@ def main():
     elif what == 'sdl2':
       build_port('sdl2')
     elif what == 'sdl2-mt':
-      shared.Settings.USE_PTHREADS = 1
+      settings.USE_PTHREADS = 1
       build_port('sdl2')
-      shared.Settings.USE_PTHREADS = 0
+      settings.USE_PTHREADS = 0
     elif what == 'sdl2-gfx':
       build_port('sdl2_gfx')
     elif what == 'sdl2-image':
       build_port('sdl2_image')
     elif what == 'sdl2-image-png':
-      shared.Settings.SDL2_IMAGE_FORMATS = ["png"]
+      settings.SDL2_IMAGE_FORMATS = ["png"]
       build_port('sdl2_image')
-      shared.Settings.SDL2_IMAGE_FORMATS = []
+      settings.SDL2_IMAGE_FORMATS = []
     elif what == 'sdl2-image-jpg':
-      shared.Settings.SDL2_IMAGE_FORMATS = ["jpg"]
+      settings.SDL2_IMAGE_FORMATS = ["jpg"]
       build_port('sdl2_image')
-      shared.Settings.SDL2_IMAGE_FORMATS = []
+      settings.SDL2_IMAGE_FORMATS = []
     elif what == 'sdl2-net':
       build_port('sdl2_net')
     elif what == 'sdl2-mixer':
-      old_formats = shared.Settings.SDL2_MIXER_FORMATS
-      shared.Settings.SDL2_MIXER_FORMATS = []
+      old_formats = settings.SDL2_MIXER_FORMATS
+      settings.SDL2_MIXER_FORMATS = []
       build_port('sdl2_mixer')
-      shared.Settings.SDL2_MIXER_FORMATS = old_formats
+      settings.SDL2_MIXER_FORMATS = old_formats
     elif what == 'sdl2-mixer-ogg':
-      old_formats = shared.Settings.SDL2_MIXER_FORMATS
-      shared.Settings.SDL2_MIXER_FORMATS = ["ogg"]
+      old_formats = settings.SDL2_MIXER_FORMATS
+      settings.SDL2_MIXER_FORMATS = ["ogg"]
       build_port('sdl2_mixer')
-      shared.Settings.SDL2_MIXER_FORMATS = old_formats
+      settings.SDL2_MIXER_FORMATS = old_formats
     elif what == 'sdl2-mixer-mp3':
-      old_formats = shared.Settings.SDL2_MIXER_FORMATS
-      shared.Settings.SDL2_MIXER_FORMATS = ["mp3"]
+      old_formats = settings.SDL2_MIXER_FORMATS
+      settings.SDL2_MIXER_FORMATS = ["mp3"]
       build_port('sdl2_mixer')
-      shared.Settings.SDL2_MIXER_FORMATS = old_formats
+      settings.SDL2_MIXER_FORMATS = old_formats
     elif what == 'freetype':
       build_port('freetype')
     elif what == 'harfbuzz':
       build_port('harfbuzz')
     elif what == 'harfbuzz-mt':
-      shared.Settings.USE_PTHREADS = 1
+      settings.USE_PTHREADS = 1
       build_port('harfbuzz')
-      shared.Settings.USE_PTHREADS = 0
+      settings.USE_PTHREADS = 0
     elif what == 'sdl2-ttf':
       build_port('sdl2_ttf')
     elif what == 'cocos2d':
       build_port('cocos2d')
     elif what == 'regal':
       build_port('regal')
     elif what == 'regal-mt':
-      shared.Settings.USE_PTHREADS = 1
+      settings.USE_PTHREADS = 1
       build_port('regal')
-      shared.Settings.USE_PTHREADS = 0
+      settings.USE_PTHREADS = 0
     elif what == 'boost_headers':
       build_port('boost_headers')
     elif what == 'mpg123':