[clang] [llvm] Fixes to unblock building LLVM and Clang as Arm64EC (PR #150068)

[Daniel Paoliello via llvm-commits]

dpaoliello wrote:

> ```
> -DCMAKE_EXE_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"
> -DCMAKE_SHARED_LINKER_FLAGS="-Xlinker /MACHINE:ARM64EC"
> ```
> 
> Does clang not pick the right MACHINE automatically? I thought we had code for that.

Trying it out now, it looks like it is working fine without this. May have been from a previous attempt when I was using `clang` and `clang++` instead of `clang-cl`.

> ```
> -DLLVM_DISABLE_ASSEMBLY_FILES=On
> ```
> 
> Probably should address this at some point, if only so people don't keep stumbling over it.

Yep, found the issue and pushed a fix.


https://github.com/llvm/llvm-project/pull/150068