ARM64ec PE files default to x86-64 when they should be aarch64

Version and Platform (required):

• Binary Ninja Version: 5.3.9409-dev Personal (0c30837b)
• Edition: Non-Commercial
• OS: Ubuntu
• OS Version: Ubuntu 25.10
• CPU Architecture: AArch64 (AmpereOne A192-32X)

Bug Description:
ARM64ec PE files are AArch64 files with x86-64 compatibility.
The COFF_Header machine field has IMAGE_FILE_MACHINE_AMD64 for compatibility, but one must continue to walking the PE64_Optional_Header in to the loadConfigTableEntry which points to eventually points to the CHPEMetadataPointer so you can get the CHPE metadata (symbol __chpe_metadata).

At this point, once you have confirmed that the CHPEMetadata entry exists, you can confirm that if the COFF header declares itself as AMD64 then it's /actually/ ARM64EC, and if the COFF header declares itself as ARM64 then it's actually ARM64X.

Some visibility in to the exact logic can be see in LLVM's source at llvm-project/llvm/include/llvm/Object/COFF.h in the getMachine() function. Additionally llvm-readobj can dump this information as well llvm-readobj --coff-load-config -r libarm64ecfex.dll as long as LLVM is 21 or newer.

Steps To Reproduce:

1. Open an arm64ec dll and see it try and disassemble as x86-64
2. Close that file, open with options and see it defaults to windows-x86_64

Expected Behavior:
I expect when loading a libarm64ecfex.dll file that is Arm64ec, that instead of default disassembling as x86-64, it instead default disassembles as aarch64.

Binary:

1. https://github.com/FEX-Emu/FEX/actions/runs/24476520323 the wine_dll_artifacts are built from our CI for every commit (but self-deletes after a couple weeks)
2. You can rip the DLL from our Ubuntu launchpad release builders. https://launchpad.net/~fex-emu/+archive/ubuntu/fex/+sourcepub/18299389/+listing-archive-extra

• https://launchpad.net/~fex-emu/+archive/ubuntu/fex/+files/fex-emu-wine_2604~q_arm64.deb Direct link to the deb

3. Or use the direct attached zip. libarm64ecfex.dll.zip
4. You could technically build an arm64ec binary yourself in msvc or llvm-mingw pretty easily but I don't have a direct example.

Additional Information:
Bonus points for parsing the CPHE config header CodeMap section, as this claims which sections in the COFF file are arm64ec, and which ones are x86-64 helper routines. Then having binja default disassemble those regions correctly with the different architectures.

Start with the attached libarm64ecfex.dll and compare its behavior with llvm-project/llvm/include/llvm/Object/COFF.h, especially the getMachine() logic and CHPE metadata handling. Use llvm-readobj --coff-load-config -r on the sample to inspect the load-config data; done means the file defaults to aarch64 rather than x86-64, with the optional CodeMap behavior evaluated separately.