/* Execute a child process. FLAGS, EXECUTABLE, ARGV, ERR are from
pex_run. IN, OUT, ERRDES, TOCLOSE are all descriptors, from
open_read, open_write, or pipe, or they are one of STDIN_FILE_NO,
/* Execute a child process. FLAGS, EXECUTABLE, ARGV, ERR are from
pex_run. IN, OUT, ERRDES, TOCLOSE are all descriptors, from
open_read, open_write, or pipe, or they are one of STDIN_FILE_NO,