The frontend, lowering and LLVM emission of an optimized executable build run in a child
process when no earlier build of the same invocation emitted its native program object.
The parent passes the LLVM text to the native helper as the file the child wrote, so the
helper runs after the pages the frontend used are released. Later builds of the
invocation find most native partitions cached and peak in the frontend, so they, along
with development builds and builds with SCRIPTC_FRONTEND_PROCESS=0, prepare their input
in-process. The child runs with the parent's Node options without --eval, --print and
their code, or inspector, watch and test runner options. With SCRIPTC_TIMING=1, it
reports its phases on the parent's clock.
Chris Tate