Implement HIE_BIOS_GHC

[pepeiborra]

Closes #270

[pepeiborra]

This is ready for review

[adamse]

Looks like this also makes a nice solution for #253

[fendor]

Ill see that I review it tomorrow.

So far the main changes are:

• remove runGhcCmd from Cradle a
• add componentRunGhcCmd for ComponentOptions
• add HIE_BIOS_GHC output variable for cradle actions.
• Adds some instances for CradleLoadResult

Did I catch most changes?

[fendor]

I am worried componentRunGhcCmd breaks Haskell Language Server - wrapper.

Afaik, the flow is as follow:

• Find hie.yaml
• Use runGhcCmd to find the ghc version
• Launch the correct HLS version

How would that work with componentRunGhcCmd?

• Find hie.yaml
• Find some component?
• Use componentRunGhcCmd to find the ghc version
• Launch the correct HLS version

[pepeiborra]

How would that work with componentRunGhcCmd?

Presumably the wrapper is always invoked with an input file, right? So the flow would be

• Find hie.yaml
• Find the local cradle
• Load the file with the cradle, resulting in some ComponentOptions
• Use componentRunGhcCmd to find the ghc version
• Launch the correct HLS version

[pepeiborra]

I assumed wrong - the wrapper is not invoked with an input file. I don't know how to solve this, it seems that tying the ghc libdir to a specific component is not a good idea after all