[Fuzzer] Migrate Fuchsia port from launchpad to fdio_spawn

fdio_spawn is the new public API for launching processes in Fuchsia.

Differential Revision: https://reviews.llvm.org/D47649

llvm-svn: 333809
GitOrigin-RevId: 8908aa4e3058aa48da01b9b3895f35de7ae82753
1 file changed