Make all shared library a relative symlink

This makes sysroot usable for cross building, it also removes the need for
_SHLIBDIRPREFIX (keeps its definition since picobsd uses it and I have no time
to test it)

Differential Revision:	https://reviews.freebsd.org/D2920
Submitted by:	imp, adrian
Tested by:	adrian

Makefile.inc1

@@ -297,7 +297,6 @@ KTMAKE=		TOOLS_PREFIX=${WORLDTMP} MAKEOBJDIRPREFIX=${WORLDTMP} \
 
 # world stage
 WMAKEENV=	${CROSSENV} \
-		_SHLIBDIRPREFIX=${WORLDTMP} \
 		_LDSCRIPTROOT= \
 		VERSION="${VERSION}" \
 		INSTALL="sh ${.CURDIR}/tools/install.sh" \
@@ -439,7 +438,6 @@ LIB32FLAGS+=		--sysroot=${WORLDTMP}
 
 # Yes, the flags are redundant.
 LIB32WMAKEENV+=	MAKEOBJDIRPREFIX=${LIB32_OBJTREE} \
-		_SHLIBDIRPREFIX=${LIB32TMP} \
 		_LDSCRIPTROOT=${LIB32TMP} \
 		VERSION="${VERSION}" \
 		INSTALL="sh ${.CURDIR}/tools/install.sh" \
@@ -2123,7 +2121,6 @@ XDTP?=/usr/${XDDIR}
 CDBENV=MAKEOBJDIRPREFIX=${MAKEOBJDIRPREFIX}/${XDDIR} \
 	INSTALL="sh ${.CURDIR}/tools/install.sh"
 CDENV= ${CDBENV} \
-	_SHLIBDIRPREFIX=${XDDESTDIR} \
 	TOOLS_PREFIX=${XDTP}
 CD2CFLAGS=-isystem ${XDDESTDIR}/usr/include -L${XDDESTDIR}/usr/lib \
 	--sysroot=${XDDESTDIR}/ -B${XDDESTDIR}/usr/libexec \

share/mk/bsd.lib.mk

@@ -362,7 +362,7 @@ _libinstall:
 .if ${_SHLIBDIR} == ${_LIBDIR}
 	${INSTALL_SYMLINK} ${SHLIB_NAME} ${DESTDIR}${_LIBDIR}/${SHLIB_LINK}
 .else
-	${INSTALL_SYMLINK} ${_SHLIBDIRPREFIX}${_SHLIBDIR}/${SHLIB_NAME} \
+	${INSTALL_RSYMLINK} ${DESTDIR}${_SHLIBDIR}/${SHLIB_NAME} \
 	    ${DESTDIR}${_LIBDIR}/${SHLIB_LINK}
 .if exists(${DESTDIR}${_LIBDIR}/${SHLIB_NAME})
 	-chflags noschg ${DESTDIR}${_LIBDIR}/${SHLIB_NAME}

share/mk/bsd.own.mk

@@ -222,9 +222,11 @@ INCLUDEDIR?=	/usr/include
 #
 HRDLINK?=	-l h
 SYMLINK?=	-l s
+RSYMLINK?=	-l rs
 
 INSTALL_LINK?=		${INSTALL} ${HRDLINK}
 INSTALL_SYMLINK?=	${INSTALL} ${SYMLINK}
+INSTALL_RSYMLINK?=	${INSTALL} ${RSYMLINK}
 
 # Common variables
 .if !defined(DEBUG_FLAGS)