The use of the SP_PATH variable under Windows is discouraged,
since Windows applications can find out for themselves where they were
started from.
SP_PATH is only used if the directory where sprt<ver>.dll
is loaded from does not contain sp<ver> (a directory),
sprt.sav, or spre.sav (where <ver> is "310" for
SICStus version 3.10(.x)). If SP_PATH is used, SICStus expects it
to be set such that %SP_PATH%\bin contains sprt.sav or
spre.sav. See Runtime Systems on Target Machines.