...but rather dynamically created (via the SDK's setsdkenv_unix.sh.in) in the
SDK's per-user output tree.  So better reflect that in instdir by putting the
symlinks into workdir/LinkTarget/Library/ instead on Mac.  (Which has the
additional benefit that the location of the symlinks doesn't change with the
versioned SDKDIRNAME.)

Change-Id: I77237f6a5d64771c3cb0866e125925ed7b0ecdaf