- Replaced several := ops with their += equivalents; the old

form became unnecessary with the bsd.prog.mk,v 1.69 change.

- Eliminated duplicate y.tab.h in SRCS.

Reviewed by:	bde

- Complementary to the said bsd.prog.mk change, use the fact
  that inner .for loops are not real loops but a tricky form
  of a local macro for the outer loop's variable, and switch
  to using faster variable modifiers to replace extensions.

share/mk/bsd.dep.mk

@@ -71,32 +71,31 @@ tags: ${SRCS}
 CLEANFILES?=
 
 .for _LSRC in ${SRCS:M*.l:N*/*}
-.for _LC in ${_LSRC:S/.l/.c/}
+.for _LC in ${_LSRC:R}.c
 ${_LC}: ${_LSRC}
 	${LEX} -t ${LFLAGS} ${.ALLSRC} > ${.TARGET}
 SRCS:=	${SRCS:S/${_LSRC}/${_LC}/}
-CLEANFILES:= ${CLEANFILES} ${_LC}
+CLEANFILES+= ${_LC}
 .endfor
 .endfor
 
 .for _YSRC in ${SRCS:M*.y:N*/*}
-.for _YC in ${_YSRC:S/.y/.c/}
+.for _YC in ${_YSRC:R}.c
 SRCS:=	${SRCS:S/${_YSRC}/${_YC}/}
-CLEANFILES:= ${CLEANFILES} ${_YC}
+CLEANFILES+= ${_YC}
 .if ${YFLAGS:M-d} != "" && ${SRCS:My.tab.h}
 .ORDER: ${_YC} y.tab.h
 ${_YC} y.tab.h: ${_YSRC}
 	${YACC} ${YFLAGS} ${.ALLSRC}
 	cp y.tab.c ${_YC}
-SRCS:=	${SRCS} y.tab.h
-CLEANFILES:= ${CLEANFILES} y.tab.c y.tab.h
+CLEANFILES+= y.tab.c y.tab.h
 .elif ${YFLAGS:M-d} != ""
-.for _YH in ${_YC:S/.c/.h/}
+.for _YH in ${_YC:R}.h
 .ORDER: ${_YC} ${_YH}
 ${_YC} ${_YH}: ${_YSRC}
 	${YACC} ${YFLAGS} -o ${_YC} ${.ALLSRC}
-SRCS:=	${SRCS} ${_YH}
-CLEANFILES:= ${CLEANFILES} ${_YH}
+SRCS+=	${_YH}
+CLEANFILES+= ${_YH}
 .endfor
 .else
 ${_YC}: ${_YSRC}