[Scons] Implement module dependency sorting.

Modules can now call:

env.module_add_dependencies(name: str, deps: list, optional: bool)

To add required or optional dependencies during the "can_build" step.

Required dependencies will be checked and the module will be not be
enabled when they are missing, printing a warning to notify the user.

methods.py

@@ -1,5 +1,6 @@
 import os
 import re
+import sys
 import glob
 import subprocess
 from collections import OrderedDict
@@ -336,7 +337,20 @@ def disable_module(self):
     self.disabled_modules.append(self.current_module)
 
 
-def module_check_dependencies(self, module, dependencies, silent=False):
+def module_add_dependencies(self, module, dependencies, optional=False):
+    """
+    Adds dependencies for a given module.
+    Meant to be used in module `can_build` methods.
+    """
+    if module not in self.module_dependencies:
+        self.module_dependencies[module] = [[], []]
+    if optional:
+        self.module_dependencies[module][1].extend(dependencies)
+    else:
+        self.module_dependencies[module][0].extend(dependencies)
+
+
+def module_check_dependencies(self, module):
     """
     Checks if module dependencies are enabled for a given module,
     and prints a warning if they aren't.
@@ -344,23 +358,41 @@ def module_check_dependencies(self, module, dependencies, silent=False):
     Returns a boolean (True if dependencies are satisfied).
     """
     missing_deps = []
-    for dep in dependencies:
+    required_deps = self.module_dependencies[module][0] if module in self.module_dependencies else []
+    for dep in required_deps:
         opt = "module_{}_enabled".format(dep)
         if not opt in self or not self[opt]:
             missing_deps.append(dep)
 
     if missing_deps != []:
-        if not silent:
-            print(
-                "Disabling '{}' module as the following dependencies are not satisfied: {}".format(
-                    module, ", ".join(missing_deps)
-                )
+        print(
+            "Disabling '{}' module as the following dependencies are not satisfied: {}".format(
+                module, ", ".join(missing_deps)
             )
+        )
         return False
     else:
         return True
 
 
+def sort_module_list(env):
+    out = OrderedDict()
+    deps = {k: v[0] + list(filter(lambda x: x in env.module_list, v[1])) for k, v in env.module_dependencies.items()}
+
+    frontier = list(env.module_list.keys())
+    explored = []
+    while len(frontier):
+        cur = frontier.pop()
+        deps_list = deps[cur] if cur in deps else []
+        if len(deps_list) and any([d not in explored for d in deps_list]):
+            # Will explore later, after its dependencies
+            frontier.insert(0, cur)
+            continue
+        explored.append(cur)
+    for k in explored:
+        env.module_list.move_to_end(k)
+
+
 def use_windows_spawn_fix(self, platform=None):
 
     if os.name != "nt":