Switching the default Haskell compiler to GHC 9.8

[PHO <pho%cielonegro.org@localhost>]

Hi all,

I'm about switch the default Haskell compiler from lang/ghc96 to 
lang/ghc98. If the new compiler doesn't work for you please let me know.

Updating GHC to 9.8 is very important on aarch64, as 9.6 had several 
compiler bugs that caused miscompilation on this architecture.

The pkgsrc GHC supports Darwin/aarch64 from now on. I'm willing to 
maintain its bootkit for the foreseeable future. However, Darwin/x86-64 
*may* be desupported at some time; my 8-years-old Intel Mac I have used 
for building bootkits is now half-broken and can stop booting any time, 
and when that happens I will lose my only machine to build Darwin/x86-64 
binaries.