[commit: ghc] wip/erikd/rts's head updated: Set `USE_MMAP` at configure time (5fae81c)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

Branch 'wip/erikd/rts' now includes:

     e4834ed Fix a performance issue with -fprint-expanded-synonyms
     c974927 Update bytestring submodule to 0.10.8.1 release tag
     7d95b20 rts: More const correct-ness fixes
     5fae81c Set `USE_MMAP` at configure time