We're currently only setting ICECC_CARET_WORKAROUND=0 when using GCC and icecc < v1.1 and not setting ICECC_REMOTE_CPP at all when using GCC. At the time, this was because we had noticed that GCC's behavior of trying to re-read original source files was not working with remote preprocessing, and we wanted to disable spurious local rebuilds when there was a compilation error.

However, there are two problems with this approach:
1. We still get spurious local rebuilds for Icecream >= v1.1
2. The workaround may hide potential issues with the compiler tarball that don't reoccur locally

Now that Ubuntu 18.04 comes with Icecream 1.3 by default, we should set that as a hard minimum version and remove our workarounds for older Icecream versions. We should also always set ICECC_CARET_WORKAROUND with GCC.