This confused quite a number of people in the past, and it is still
slightly annoying to always switch the directory when testing both the
OS and the fuzzer build. Instead, let's just switch to the correct
directory automatically.
This is a start to properly letting us cross-compile Lagom where both
the Tools and the BUILD_LAGOM=ON build are using Lagom CMakeLists.
The initial cut allows an Android build to succeed, more or less.
But there are issues with namespace clashes when using FetchContent with
this approach.
This allows us to fuzz the generated unicode and timezone database
helpers, and to fuzz things like LibJS using Fuzzilli to get proper
coverage of our unicode handling code.
Update the Azure CI to use the new two-stage build as well, and cleanup
some unused CMake options there.
