only error combining +whole-archive and +bundle for rlibs
Fixes https://github.com/rust-lang/rust/issues/110912
Checking `flavor == RlibFlavor::Normal` was accidentally lost in 601fc8b36bhttps://github.com/rust-lang/rust/pull/105601
That caused combining +whole-archive and +bundle link modifiers on non-rlib crates to fail with a confusing error message saying that combination is unstable for rlibs. In particular, this caused the build to fail when +whole-archive was used on staticlib crates, even though +whole-archive effectively does nothing on non-bin crates because the final linker invocation is left to an external build system.
cc ``@petrochenkov``