[lldb] Treat ARM64X images as ARM64.

With D149091, ARM64X binaries are no longer reported as ARM64. This broke
lldb tests as Windows 11 system DLLs are mostly ARM64X binaries and lldb
doesn't know how to handle them. Ideally lldb would understand a bit more
about ARM64X and handle them as AMD64 in x64 processes, but this is
enough to preserve previous behavior and fix tests.

Reviewed By: mstorsjo
Differential Revision: https://reviews.llvm.org/D156268