[win][arm64ec] XFAIL x64 intrinsic tests on Arm64EC (#153474)HEADmain

Clang defines the x64 preprocessor macro (`__x86_64__`) when building
Arm64EC, however the tests for x64 built-ins and intrinsics are
currently failing since the relevant functions don't exist, resulting in
errors like:

```
Line 165: invalid conversion between vector type '__v2di' (vector of 2 'long long' values) and integer type 'int' of different size
```

(Clang doesn't know the intrinsics being called, and so treats it like
an undefined function, which makes it assume the return type is `int`)

For now, expect these tests to fail until someone decides to implement
these intrinsics.

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