pkg/build: fix config parsing for gVisor
pkg/build: fix config parsing for gVisor

In the previous method, string comparisons did not work properly for the
last flag because it is followed by a newline character.

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