...after cfd2691e "[API CHANGE] Remove salcpprt
static library" had removed the sole regular File item from gid_Dir_Lib_Sdk,
leaving only Unixlink items.  But the solenv/bin/modules/installer.pm code used
to only auto-create any directories that contain regular Files.  Changed that to
also consider Unixlinks in addition to regular Files.

And to add insult to injury, the code in
solenv/bin/modules/installer/simplepackage.pm creating the actual symlinks
represented by the Unixlink items silently does nothing when a symlink cannot be
created (because the partent dir is missing).  To be fixed in another follow-up
commit.

Change-Id: Ic7a682a17ac59c789c85c56c825dd623bc59428c