tools/syz-build: add tracing mode
tools/syz-build: add tracing mode

Add -trace flag that enabled build process tracing and saving of debug artefacts.
Useful for debugging of #2297.

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