Make sure the DTrace header files are built before depend and before

the build starts.

This adds a new variable DHDRS that contains a list of all DTrace
header files.  Then, we use the beforedepend hook to make sure the
heaeder files are built.

Introduce a beforebuild dependency (from projects/bmake) based on
feedback from Simon J. Gerraty.  This lets us generate the header
files without running make depend.

Reviewed by:	sjg, imp
MFC after:	3 days

share/mk/bsd.dep.mk

@@ -129,6 +129,7 @@ CFLAGS+=	-D_DTRACE_VERSION=1 -I${.OBJDIR}
 .endif
 .for _DSRC in ${SRCS:M*.d:N*/*}
 .for _D in ${_DSRC:R}
+DHDRS+=	${_D}.h
 ${_D}.h: ${_DSRC}
 	${DTRACE} -xnolibs -h -s ${.ALLSRC}
 SRCS:=	${SRCS:S/${_DSRC}/${_D}.h/}
@@ -148,6 +149,8 @@ ${_D}.po: ${_D}.h ${POBJS:S/${_D}.po//}
 .endif
 .endfor
 .endfor
+beforedepend: ${DHDRS}
+beforebuild: ${DHDRS}
 .endif
 
 .if !target(depend)

share/mk/bsd.lib.mk

@@ -118,7 +118,8 @@ PO_FLAG=-pg
 	${CC} ${PICFLAG} -DPIC ${CFLAGS} ${ACFLAGS} -c ${.IMPSRC} -o ${.TARGET}
 	${CTFCONVERT_CMD}
 
-all: objwarn
+all: beforebuild .WAIT
+beforebuild: objwarn
 
 .if defined(PRIVATELIB)
 _LIBDIR:=${LIBPRIVATEDIR}

share/mk/bsd.prog.mk

@@ -159,7 +159,8 @@ MAN1=	${MAN}
 .endif
 .endif # defined(PROG)
 
-all: objwarn ${PROG} ${SCRIPTS}
+all: beforebuild .WAIT ${PROG} ${SCRIPTS}
+beforebuild: objwarn
 .if ${MK_MAN} != "no"
 all: _manpages
 .endif