SCons: Disable Clang -Wordered-compare-function-pointers warning

It's raised for us on many comparators implemented to be able to store a struct
in `Set` or `Map` (who rely on `operator<` internally). In the cases I reviewed
we don't actually care about the ordering and we use the struct's function
pointers as that's the only distinctive data available.

(cherry picked from commit 802810c371a1b0952a3d830e2f5488010f5102b4)
(cherry picked from commit 4c79dcc3e70b677047582e8559a536f1cfec3c5a)

SConstruct

@@ -407,18 +407,21 @@ if selected_platform in platform_list:
     else:  # Rest of the world
         version = methods.get_compiler_version(env) or [-1, -1]
 
-        shadow_local_warning = []
-        all_plus_warnings = ["-Wwrite-strings"]
+        common_warnings = []
 
         if methods.using_gcc(env):
-            env.Append(CCFLAGS=["-Wno-misleading-indentation"])
+            common_warnings += ["-Wno-misleading-indentation"]
             if version[0] >= 7:
-                shadow_local_warning = ["-Wshadow-local"]
+                common_warnings += ["-Wshadow-local"]
+        elif methods.using_clang(env):
+            # We often implement `operator<` for structs of pointers as a requirement
+            # for putting them in `Set` or `Map`. We don't mind about unreliable ordering.
+            common_warnings += ["-Wno-ordered-compare-function-pointers"]
 
         if env["warnings"] == "extra":
             # Note: enable -Wimplicit-fallthrough for Clang (already part of -Wextra for GCC)
             # once we switch to C++11 or later (necessary for our FALLTHROUGH macro).
-            env.Append(CCFLAGS=["-Wall", "-Wextra", "-Wno-unused-parameter"] + all_plus_warnings + shadow_local_warning)
+            env.Append(CCFLAGS=["-Wall", "-Wextra", "-Wwrite-strings", "-Wno-unused-parameter"] + common_warnings)
             env.Append(CXXFLAGS=["-Wctor-dtor-privacy", "-Wnon-virtual-dtor"])
             if methods.using_gcc(env):
                 env.Append(
@@ -434,9 +437,9 @@ if selected_platform in platform_list:
                 if version[0] >= 9:
                     env.Append(CCFLAGS=["-Wattribute-alias=2"])
         elif env["warnings"] == "all":
-            env.Append(CCFLAGS=["-Wall"] + shadow_local_warning)
+            env.Append(CCFLAGS=["-Wall"] + common_warnings)
         elif env["warnings"] == "moderate":
-            env.Append(CCFLAGS=["-Wall", "-Wno-unused"] + shadow_local_warning)
+            env.Append(CCFLAGS=["-Wall", "-Wno-unused"] + common_warnings)
         else:  # 'no'
             env.Append(CCFLAGS=["-w"])
         if env["werror"]: