Use .MAKE.LEVEL being defined as a bootstrap aid when providing

fallback targets to build the aic generated files. fmake doesn't like
the current construct, and since it doesn't have .MAKE.LEVEL, just
don't provide the fallback targets for fmake. This gives a little
extra compatibility to old systems trying to build new kernels at
almost no cost to the current code.

sys/modules/aic7xxx/ahc/Makefile

@@ -35,7 +35,11 @@ ${GENSRCS}:								 \
 			${REG_PRINT_OPT}				 \
 			-i ${SYSDIR}/dev/aic7xxx/aic7xxx_osm.h \
 			${SYSDIR}/dev/aic7xxx/aic7xxx.seq
-.else
+.elif defined(.MAKE.LEVEL)
+# This target interfers with fmake's world view and causes this message
+# to appear when building the tree from 8.x worlds where fmake is the
+# default. fmake doens't define .MAKE.LEVEL so key off that to omit it,
+# while still allowing more-modern makes to theoretically update things.
 ${GENSRCS}:
 	@echo "Error: ${.TARGET} is missing.  Run 'make ahcfirmware'"
 .endif