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)

SConstruct

@@ -425,17 +425,21 @@ if selected_platform in platform_list:
     else:  # GCC, Clang
         version = methods.get_compiler_version(env) or [-1, -1]
 
-        gcc_common_warnings = []
+        common_warnings = []
 
         if methods.using_gcc(env):
-            gcc_common_warnings += ["-Wno-misleading-indentation"]
+            common_warnings += ["-Wno-misleading-indentation"]
             if version[0] >= 7:
-                gcc_common_warnings += ["-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", "-Wwrite-strings", "-Wno-unused-parameter"] + gcc_common_warnings)
+            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(
@@ -451,9 +455,9 @@ if selected_platform in platform_list:
                 if version[0] >= 9:
                     env.Append(CCFLAGS=["-Wattribute-alias=2"])
         elif env["warnings"] == "all":
-            env.Append(CCFLAGS=["-Wall"] + gcc_common_warnings)
+            env.Append(CCFLAGS=["-Wall"] + common_warnings)
         elif env["warnings"] == "moderate":
-            env.Append(CCFLAGS=["-Wall", "-Wno-unused"] + gcc_common_warnings)
+            env.Append(CCFLAGS=["-Wall", "-Wno-unused"] + common_warnings)
         else:  # 'no'
             env.Append(CCFLAGS=["-w"])