Add THREADS_ENABLED macro in order to compile Godot to run on the main thread

SConstruct

@@ -183,6 +183,7 @@ opts.Add(BoolVariable("separate_debug_symbols", "Extract debugging symbols to a
 opts.Add(EnumVariable("lto", "Link-time optimization (production builds)", "none", ("none", "auto", "thin", "full")))
 opts.Add(BoolVariable("production", "Set defaults to build Godot for use in production", False))
 opts.Add(BoolVariable("generate_apk", "Generate an APK/AAB after building Android library by calling Gradle", False))
+opts.Add(BoolVariable("threads", "Enable threading support", True))
 
 # Components
 opts.Add(BoolVariable("deprecated", "Enable compatibility code for deprecated and removed features", True))
@@ -832,6 +833,10 @@ if selected_platform in platform_list:
         suffix += ".double"
 
     suffix += "." + env["arch"]
+
+    if not env["threads"]:
+        suffix += ".nothreads"
+
     suffix += env.extra_suffix
 
     sys.path.remove(tmppath)
@@ -972,6 +977,9 @@ if selected_platform in platform_list:
         env.Tool("compilation_db")
         env.Alias("compiledb", env.CompilationDatabase())
 
+    if env["threads"]:
+        env.Append(CPPDEFINES=["THREADS_ENABLED"])
+
     Export("env")
 
     # Build subdirs, the build order is dependent on link order.