[llvm][aarch64] Fix Arm64EC name mangling algorithm (#115567)

Arm64EC uses a special name mangling mode that adds `$$h` between the
symbol name and its type. In MSVC's name mangling `@` is used to
separate the name and type BUT it is also used for other purposes, such
as the separator between paths in a fully qualified name.

The original algorithm was quite fragile and made assumptions that
didn't hold true for all MSVC mangled symbols, so instead of trying to
improve this algorithm we are now using the demangler to indicate where
the insertion point should be (i.e., to parse the fully-qualified name
and return the current string offset).

Also fixed `isArm64ECMangledFunctionName` to search for `@$$h` since the
`$$h` must always be after a `@`.

Fixes #115231

0 files changed, 0 insertions, 0 deletions