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/libalias/libalias/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-.PATH: ${.CURDIR}/../../../sys/netinet/libalias
+.PATH: ${SRCTOP}/sys/netinet/libalias
 
 PACKAGE=lib${LIB}
 LIB=	alias

lib/libalias/modules/Makefile

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-.include "${.CURDIR}/../../../sys/modules/libalias/modules/modules.inc"
+.include "${SRCTOP}/sys/modules/libalias/modules/modules.inc"
 
 SUBDIR=	${MODULES}
 

lib/libalias/modules/Makefile.inc

@@ -1,6 +1,6 @@
 # $FreeBSD$
 
-.PATH: ${.CURDIR}/../../../../sys/netinet/libalias
+.PATH: ${SRCTOP}/sys/netinet/libalias
 
 SHLIBDIR?= /lib
 LIB?=   alias_${NAME}