Add support for global_ctor

[gavrilikhin-d]

Need to initialize global variables with non-constant expressions.
This is usually done by using llvm's global_ctor array.
Can't find an API for using it in inkwell

[TheDan64]

Is there a llvm sys method for it?

[gavrilikhin-d]

Looks like LLVM doesn't expose append_to_global_ctors or append_to_global_dtors to C API.
https://llvm.org/doxygen/ModuleUtils_8h.html

So there is nothing in llvm sys too.

[gavrilikhin-d]

However, @llvm.global_ctors is a plain global variable, so it's still possible to create it manually
https://llvm.org/docs/LangRef.html#the-llvm-global-dtors-global-variable

[TheDan64]

Ok to close this issue then? Sounds like there's nothing we can do