v0.15.14

Bugfixes:

• Fix a compilation memory regression for very large files (#4521 by @mjrussell)

  When compiling a a very large file (>12K lines)
  the CSE pass could balloon memory and result in increased
  compilation times.

  This fix uses a strict Map instead of a lazy Map to avoid
  building up unnecessary thunks during the optimization pass.

• Fix two space leaks while compiling many modules (#4517 by @MonoidMusician)

  The first would interleave compilation of too many modules at once, which
  would increase memory usage, especially for single threaded builds with
  +RTS -N1 -RTS. Now the number of concurrent modules is limited to
  the number of threads available to the
  GHC runtime system.

  The second would hold on to memory from modules that compiled with warnings
  until the end of the build when the warnings were printed and the memory freed.
  This is now fixed with additional NFData instances.