Use SRCTOP-relative paths to other directories instead of .CURDIR-relative ones

This implifies pathing in make/displayed output

MFC after:	3 weeks
Sponsored by:	Dell EMC Isilon

lib/libpam/libpam/Makefile

@@ -36,7 +36,7 @@
 # $FreeBSD$
 
 PACKAGE=lib${LIB}
-OPENPAM=	${.CURDIR}/../../../contrib/openpam
+OPENPAM=	${SRCTOP}/contrib/openpam
 .PATH: ${OPENPAM}/include ${OPENPAM}/lib/libpam ${OPENPAM}/doc/man
 
 # static_libpam will build libpam.a

lib/libpam/static_libpam/Makefile

@@ -35,7 +35,7 @@
 #
 # $FreeBSD$
 
-.PATH: ${.CURDIR}/../libpam
+.PATH: ${SRCTOP}/lib/libpam
 
 # Only build the static library.
 LIB=	pam
@@ -66,4 +66,4 @@ CLEANFILES+=	openpam_static.o \
 openpam_static_modules.o: openpam_static.o ${STATIC_MODULES}
 	${CC} -nostdlib ${CFLAGS} -o ${.TARGET} -r -Wl,--whole-archive ${.ALLSRC}
 
-.include "${.CURDIR}/../libpam/Makefile"
+.include "${.CURDIR:H}/libpam/Makefile"