The previous default was Deployable though it was being
overridden to Wrapper in the ghc shell script wrapper.

It's still possible to override it, just use -optl-Wl,-soname, eg:
ghc -shared -dynamic foo.o -o libfoo.so -optl-Wl,-soname,libbar.so

Previously the object code for the C main function lived in the rts
lib, however this is a problem when the rts is built as a shared lib.
With Windows DLLs it always causes problems while on ELF systems it's a
problem when the user decides to use their own C main function rather
than a Haskell Main.main. So instead we now put main in it's own tiny
little static lib libHSrtsmain.a which we install next to the rts libs.
Whenever ghc links a program (without -no-hs-main) then it also links
in -lHSrtsmain. For consistency we always do it this way now rather
than trying to do it differently for static vs shared libraries.

We now do it for all ways and for all platforms. This was a Windows-only
version that only kept a separate Main.dyn_o for the dynamic linking case.
It had to do that because Windows DLLs are stricter about unresolved symbols
where as for ELF platforms we only run into the problem when we're not using
a Haskell main function.

and document primOpHasSideEffects

libraries built by stage2 need all their bits in the bindist too.
We were testing (stage == 1) rather than (stage /= 0).