build: further prevent non-lbmk-work-directoryHEADmaster

this is a follow-up to the previous commit

again, there's no posix way to check the path to the
file at argument 0, because readlink (utility) isn't
defined in posix (the C function is defined, but not
the utility included on many unices)

check whether "build" (file) exists, and whether it
is a symlink; if the latter, then we are definitely
not in the lbmk work directory!

Signed-off-by: Leah Rowe <leah@libreboot.org>

0 files changed, 0 insertions, 0 deletions