SCons: Bump minimum SCons & Python versions

SCons: 3.1.2 → 4.0
Python: 3.6 → 3.8

SConstruct

@@ -1,8 +1,8 @@
 #!/usr/bin/env python
 from misc.utility.scons_hints import *
 
-EnsureSConsVersion(3, 1, 2)
-EnsurePythonVersion(3, 6)
+EnsureSConsVersion(4, 0)
+EnsurePythonVersion(3, 8)
 
 # System
 import atexit
@@ -1060,13 +1060,6 @@ if env["vsproj"]:
     env.vs_srcs = []
 
 if env["compiledb"]:
-    if env.scons_version < (4, 0, 0):
-        # Generating the compilation DB (`compile_commands.json`) requires SCons 4.0.0 or later.
-        print_error(
-            "The `compiledb=yes` option requires SCons 4.0 or later, but your version is %s." % scons_raw_version
-        )
-        Exit(255)
-
     env.Tool("compilation_db")
     env.Alias("compiledb", env.CompilationDatabase())