Fix arm64 build when using Clang

The commit b5a8055b5c should target GCC builds only as
-flax-vector-conversions has different behaviour in Clang and is
currently making the build fail.

Signed-off-by: Filipe Rinaldi <filipe.rinaldi@gmail.com>
(cherry picked from commit 2841144096)

modules/raycast/SCsub

@@ -90,7 +90,7 @@ if env["builtin_embree"]:
 
     if not env.msvc:
         # Flags synced with upstream gnu.cmake.
-        if env["arch"] == "arm64" and env["platform"] == "x11":
+        if env["arch"] == "arm64" and env["platform"] == "x11" and not env["use_llvm"]:
             env_thirdparty.Append(CXXFLAGS=["-flax-vector-conversions"])
 
         env_thirdparty.Append(