[NVPTX] Add support for calling aliases (#81170)

The current implementation of aliases tries to remove all the aliases in
the module to prevent the generic version of `AsmPrinter` from emitting
them incorrectly. Unfortunately, if the aliases are used this will fail.
Instead let's override the function to print aliases directly.

In addition, the declarations of the alias functions must occur before
the uses. To fix this we emit alias declarations as part of
`emitDeclarations` and only emit the `.alias` directives at the end
(where we can assume the aliasee has also already been declared).