For performance reasons the reproducers don't copy the files captured by
the file collector eagerly, but wait until the reproducer needs to be
generated.
This is a problematic when LLDB crashes and we have to do all this
signal-unsafe work in the signal handler. This patch uses a similar
trick to clang, which has the driver invoke a new cc1 instance to do all
this work out-of-process.
This patch moves the writing of the mapping file as well as copying over
the reproducers into a separate process spawned when lldb crashes.
Differential revision: https://reviews.llvm.org/D89600
Jonas Devlieghere