[build] Unconditionally pull x64 clang on Windows.

The status quo works for the wrong reason: the Windows ARM64 machines are running x64 Python.

Change-Id: I8c31c953109700f5c0187766b6f46190d63a5a7f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/308243
Reviewed-by: Alexander Aprelev <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

DEPS

@@ -517,7 +517,7 @@ deps = {
               "version": Var("clang_version"),
           },
       ],
-      "condition": "host_cpu == x64 and host_os == win",
+      "condition": "host_os == win", # On ARM64 Windows too because Fuchsia doesn't provide the host-arm64 toolchain.
       "dep_type": "cipd",
   },
   Var("dart_root") + "/buildtools/linux-arm64/clang": {