[llvm] [offload] lazily load liboffload (PR #221731)

[Alex Duran via llvm-commits]

adurang wrote:

> > > We need to pass a list of backends to olInit to avoid initialazing all of them. But to know which backends to use, we need to know which backends are compatible with the images in the binary with olIsValidBinary. But that requires olInit to be called first, ....
> > 
> > 
> > I thought that corresponding `ol` function that did that did not require the runtime to be initialized for this reason, maybe I'm remembering wrong.
> 
> The first parameter is a device handle, which we can only obtain after olInit afaik.

One thing is that liboffload only seems to use isDeviceCompatible. I don't see any API that allows to use isPluginCompatible.

https://github.com/llvm/llvm-project/pull/221731