When targeting arm64e, vtable pointers are signed with a discriminator
that incorporates the object's address
(PointerAuthVTPtrAddressDiscrimination) and class type
(PointerAuthVTPtrTypeDiscrimination).
I had to make a small change to clang, specifically in
getPointerAuthDeclDiscriminator(). Previously, that was computing the
discriminator based on getMangledName(). The latter returns the
AsmLabelAttr, which for functions imported by lldb, is prefixed with
`$__lldb_func`, causing a different discriminator to be generated.
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