FAST_DEPEND: Only pass -MF if we care about the object being compiled.

This will save time generating dependency files that we didn't expect
due to cases where SRCS!=OBJS or for building custom targetted objects
in Makefiles that do not end up in the DEPENDOBJS list.

This uses a bmake trick to modify CFLAGS based on ${.TARGET}.  A
.PARSEDIR check is done for the sake of MFC safety.

MFC after:	2 weeks
Sponsored by:	EMC / Isilon Storage Division

share/mk/bsd.dep.mk

@@ -158,7 +158,14 @@ DEPEND_MP?=	-MP
 DEPEND_FILTER=	C,/,_,g
 DEPEND_CFLAGS+=	-MD ${DEPEND_MP} -MF${DEPENDFILE}.${.TARGET:${DEPEND_FILTER}}
 DEPEND_CFLAGS+=	-MT${.TARGET}
+.if defined(.PARSEDIR)
+# Only add in DEPEND_CFLAGS for CFLAGS on files we expect from DEPENDOBJS
+# as those are the only ones we will include.
+DEPEND_CFLAGS_CONDITION= !empty(DEPENDOBJS:M${.TARGET:${DEPEND_FILTER}})
+CFLAGS+=	${${DEPEND_CFLAGS_CONDITION}:?${DEPEND_CFLAGS}:}
+.else
 CFLAGS+=	${DEPEND_CFLAGS}
+.endif
 DEPENDSRCS=	${SRCS:M*.[cSC]} ${SRCS:M*.cxx} ${SRCS:M*.cpp} ${SRCS:M*.cc}
 .if !empty(DEPENDSRCS)
 DEPENDOBJS+=	${DEPENDSRCS:R:S,$,.o,}

share/mk/bsd.lib.mk

@@ -182,6 +182,7 @@ lib${LIB_PRIVATE}${LIB}.a: ${OBJS} ${STATICOBJS}
 .if ${MK_PROFILE} != "no" && defined(LIB) && !empty(LIB)
 _LIBS+=		lib${LIB_PRIVATE}${LIB}_p.a
 POBJS+=		${OBJS:.o=.po} ${STATICOBJS:.o=.po}
+DEPENDOBJS+=	${POBJS}
 CLEANFILES+=	${POBJS}
 
 lib${LIB_PRIVATE}${LIB}_p.a: ${POBJS}
@@ -194,6 +195,7 @@ lib${LIB_PRIVATE}${LIB}_p.a: ${POBJS}
 .if defined(SHLIB_NAME) || \
     defined(INSTALL_PIC_ARCHIVE) && defined(LIB) && !empty(LIB)
 SOBJS+=		${OBJS:.o=.So}
+DEPENDOBJS+=	${SOBJS}
 CLEANFILES+=	${SOBJS}
 .endif