[sanitizer_common] Close superfluous file descriptors in spawned process
Use attribute flag POSIX_SPAWN_CLOEXEC_DEFAULT in the call to
If this flag is set, then only file descriptors explicitly described by
the file_actions argument are available in the spawned process; all of
the other file descriptors are automatically closed in the spawned
POSIX_SPAWN_CLOEXEC_DEFAULT is an Apple-specific extension.