Revert "Add compiler-rt to build."

[cbuttner]

Reverts #4

cmake --build . --target install fails. The resulting package is incomplete.

[lerno]

The solution is probably to make two different compilations. But does this at least create the compiler-rt?

[cbuttner]

Yes this builds it correctly, just the install is messed up.
I don't know if a separate compilation will fix the install, but if not then we'll just have to copy the relevant files manually.