GHCi linker should run constructors for linked libraries

[pumpkin]

As far as I can tell from my experimentation, any library that contains a function with attribute((constructor)) on it won't have its constructor(s) run when loaded, or its destructors run when unloaded. This violates assumptions that some libraries make.

[simonmar]

see also #5386

Note that if you put the constructor in a shared library (.so or .dll) then the constructor will be run when the library is loaded, because GHCi invokes the system linker for these.

[igloo]

See also #3333.

[simonpj]

There is real work here, to fix our DIY linker to run constructors when we dynamically load static libraries in GHCi. Our ultimate goal is to do dynamic linking by default, so then we wouldn't have any static libraries, and this whole issue would go away.

So we're punting to 7.6.

Simon

[simonmar]

Would be fixed by #3658.

[igloo]

We plan to fix this by switching to dynamic linking