Allow profile builds

[mgajda]

Profiling requires special library flavour (usually p_dyn or p_dyn_thr), but is necessary for performance debugging.

Currently attempting to build with ghc-options like -prof -fprof-auto gives the following message:

$ pier build -j12
call-stack-0.1.0: building library
hspec-discover-2.4.8: building library
mtl-2.2.2: building library
setenv-0.1.1.3: building library
primitive-0.6.3.0: building library
random-1.1: building library
split-0.2.3.3: building library
stm-2.4.5.0: building library
Error when running Shake build system:
* Library xeno
* Library hspec
* Library call-stack
* Command: call-stack-0.1.0: building library

_pier/artifact/gSZoS8GQJgmJql5LGw0vk45lAMYeuyJbEMq18RyyLK8/package/raw/call-stack-0.1.0/src/Data/SrcLoc.hs:2:8: error:
    Could not find module ‘Prelude’
    Perhaps you haven't installed the "p_dyn" libraries for package ‘base-4.10.1.0’?
    Use -v to see a list of the files searched for.
  |
2 | module Data.SrcLoc (SrcLoc(..)) where
  |        ^^^^^^^^^^^

_pier/artifact/gSZoS8GQJgmJql5LGw0vk45lAMYeuyJbEMq18RyyLK8/package/raw/call-stack-0.1.0/src/Data/SrcLoc.hs:5:1: error:
    Could not find module ‘GHC.Stack’
    Perhaps you haven't installed the "p_dyn" libraries for package ‘base-4.10.1.0’?
    Use -v to see a list of the files searched for.
  |
5 | import           GHC.Stack (SrcLoc(..))
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^