Bug 1681582 - Disable Rust CFG on aarch64-windows r=firefox-build-system-reviewers,mhentges

This is bug 1639318 all over again except from Rust rather than C++. It's the same symptom, nsXPTCStub vtables aren't marked as valid targets.

In the earlier bug we disabled CFG for C++ on ARM64. Let's do the same for Rust. According to that bug, "It's not clear why this doesn't happen on x86 builds. Given priorities, I can't really justify investigating this, although I suspect that fixing the underlying issue would be pretty much bug 1483885."

Differential Revision: https://phabricator.services.mozilla.com/D99278

build/moz.configure/toolchain.configure

@@ -2185,7 +2185,8 @@ def rust_compile_flags(opt_level, debug_rust, target, debug_symbols, frame_point
         opts.append("debuginfo=%s" % debug_info)
     if frame_pointers:
         opts.append("force-frame-pointers=yes")
-    if target.kernel == "WINNT":
+    # CFG for arm64 is crashy, see `def security_hardening_cflags`.
+    if target.kernel == "WINNT" and target.cpu != "aarch64":
         opts.append("control-flow-guard=yes")
 
     flags = []