relocatable: support UNIXROOT in relocate() on EMX

UNIXROOT is used to specify a drive of a root of FHS. So if a path is
started with '/', then it should be translated to "$UNIXROOT/".

* lib/relocatable.c (relocate): Prepend $UNIXROOT to pathname if it is
started with '/' on EMX.
posixtm: avoid compiler warning in a better way

* lib/posixtm.c (IF_LINT): Remove.
(year, posix_time_parse):
Return true (not 0) if successful.  All callers changed.
(posix_time_parse): Simplify to pacify GCC without need for IF_LINT.