instead of running pwd all the time, run it once in lib.sh,
and export PWD.
for cbmk-specific use of PWD, use xbmkpwd, which contains
the value of PWD as was set by the pwd utility in lib.sh.
many parts of cbmk rely on pwd, and it *must* be correct.
this change adds basic error handling, since pwd can in
fact return errors in some cases.
Signed-off-by: Leah Rowe <leah@libreboot.org>
12e600bf5c