While compiling the `record` package with ghc-8 rc3 with `stack build`, the memory usage went above 6gb and started trashing. But when `stack build --fast` (-O0) was being used the package compiled with maximum memory at 1.8gb.

Also `stack build` works fine with ghc-7.10.3 with the build taking about 1.7gb. Attached is the stack file to reproduce the issue.

Steps to reproduce:

1. Create a new directory and put the attached stack.yaml there.

2. run `stack build` - this will thrash after some time