[Bug target/104957] [nvptx] Use .alias directive (available starting ptx isa version 6.3)

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104957

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
So, what do we get after specifying -malias -mptx=6.3?

Alias attribute only for functions, not variables.

No support for weak alias (allowing this does compile, but we run into
execution fails in gcc.dg/globalalias.c and gcc.dg/pr77587.c).

No support for aliases of weak functions.  We can't detect this in the
compiler, so we'll run into linker error "error: Function test with .weak scope
cannot be aliased".