build,win: bail vcbuild if mklink fails
Refs: https://github.com/nodejs/node/pull/27149#issuecomment-482811243
Otherwise vcbuild will continue even if mklink
fails, and will use old artifacts if present.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines