math/slatec: fix installation
Port uses <bsd.lib.mk>, which desires STRIP=${STRIP}, but we have
started to set STRIP=${STRIP_CMD} in MAKE_ENV a while ago.
Override this bogus setting in MAKE_ARGS to fix installation.
MFH: 2026Q2
See also: D55509
(cherry picked from commit dc486d439f829b95b71be83052a2fb4bdf5a8a75)