+# as we stick to -e, CLEARENV ensures that local variables in lower
+# Makefiles remain local and variable. $${VAR+VAR} is tribute to Korn
+# shell, which [annoyingly enough] terminates unset with error if VAR
+# is not present:-( TOP= && unset TOP is tribute to HP-UX /bin/sh,
+# which terminates unset with error if no variable was present:-(
+CLEARENV= TOP= && unset TOP $${LIB+LIB} $${LIBS+LIBS} \
+ $${INCLUDE+INCLUDE} $${INCLUDES+INCLUDES} \
+ $${DIR+DIR} $${DIRS+DIRS} $${SRC+SRC} \
+ $${LIBSRC+LIBSRC} $${LIBOBJ+LIBOBJ} $${ALL+ALL} \
+ $${EXHEADER+EXHEADER} $${HEADER+HEADER} \
+ $${GENERAL+GENERAL} $${CFLAGS+CFLAGS} \
+ $${ASFLAGS+ASFLAGS} $${AFLAGS+AFLAGS} \
+ $${LDCMD+LDCMD} $${LDFLAGS+LDFLAGS} \
+ $${SHAREDCMD+SHAREDCMD} $${SHAREDFLAGS+SHAREDFLAGS} \
+ $${SHARED_LIB+SHARED_LIB} $${LIBEXTRAS+LIBEXTRAS}
+