This makes the LLDB fuzzers write their fuzzer artifacts to
their own directory in the build directory. It also adds an artifact
prefix to the target fuzzer to make it easier to tell which fuzzer
wrote the artifact.
Differential revision: https://reviews.llvm.org/D128450
Create a ninja target for running the LLDB target fuzzer.
Currently the ninja target for the fuzzer will build the fuzzer without
running it. This allows the fuzzer to be built and run.
Differential revision: https://reviews.llvm.org/D127882