rustc: Fix mixing crates with different `share_generics`
This commit addresses #64319 by removing the `dylib` crate type from the
list of crate type that exports generic symbols. The bug in #64319
arises because a `dylib` crate type was trying to export a symbol in an
uptream crate but it miscalculated the symbol name of the uptream
symbol. This isn't really necessary, though, since `dylib` crates aren't
that heavily used, so we can just conservatively say that the `dylib`
crate type never exports generic symbols, forcibly removing them from
the exported symbol lists if were to otherwise find them.
The fix here happens in two places:
* First is in the `local_crate_exports_generics` method, indicating that
it's now `false` for the `Dylib` crate type. Only rlibs actually
export generics at this point.
* Next is when we load exported symbols from upstream crate. If, for our
compilation session, the crate may be included from a dynamic library,
then its generic symbols are removed. When the crate was linked into a
dynamic library its symbols weren't exported, so we can't consider
them a candidate to link against.
Overally this should avoid situations where we incorrectly calculate the
upstream symbol names in the face of differnet `share_generics` options,
ultimately...
Closes#64319
40fae88fa8