Itanium Mangling: Mangle `__alignof__` differently than `alignof`.

The two operations have acted differently since Clang 8, but were
unfortunately mangled the same. The new mangling uses new "vendor
extended expression" syntax proposed in

GCC had the same mangling problem,, and
will hopefully be switching to the same mangling as implemented here.

Additionally, fix the mangling of `__uuidof` to use the new extension
syntax, instead of its previous nonstandard special-case.

Adjusts the demangler accordingly.

Differential Revision:

GitOrigin-RevId: 9c7aeaebb3ac1b94200b59b111742cb6b8f090c2
2 files changed