Compiler should be upgraded before build #71
Description
Before building any packages, we should upgrade any packages that come pre-installed on the bootstrap VM and affect the content of the packages that are built. For example, we should upgrade GCC and Clang/LLVM, so that we have any security or functional fixes that might have been shipped.
The simplest way to do this might just be to run apt upgrade, and upgrade all of the packages installed. This can take a couple minutes to run currently, but we could decrease the impact by updating the bootstrap image every so often (maybe every few months) so that there are fewer packages to upgrade.