dlmopen with RTLD_GLOBAL

[Vivek Das Mohapatra]

> I've been looking for some users to prioritize this work :-)

I have a use case -

I posted here earlier about the segregated linking work I've been doing
built on top of dlmopen() for improved steam runtime portability.

I've got a more detailed write-up in progress here:
https://people.collabora.com/~vivek/dynamic-linking/monkeypatched-dynamic-linking.pdf

I curently have to do some tricks with patchelf to enable older (pre v17.x) 
versions of Mesa with the segregated linker, but a working dlmopen+RTLD_GLOBAL
would make my life easier.