sys/syz-sysgen: add -src and -out flags
sys/syz-sysgen: add -src and -out flags

This is useful for integrating into Fuchsia's build system, where we
need to be able to run syz-sysgen with a read-only source directory,
and emit the output files elsewhere.

google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller