don't add -R/usr/lib link option even with --enable-rpath

configure.ac

@@ -306,8 +306,7 @@ fi
 
 AX_CHECK_ZLIB([
    AC_SUBST([ZLIB],[-lz])
-   r=""
-   test "$enable_rpath" = yes && r=" -R${ZLIB_HOME}/lib"
+   r=""; test "$enable_rpath" = yes -a "$ZLIB_HOME" != /usr && r=" -R${ZLIB_HOME}/lib"
    AC_SUBST([ZLIB_LDFLAGS],["-L${ZLIB_HOME}/lib$r"])
    AC_SUBST([ZLIB_CPPFLAGS],["-I${ZLIB_HOME}/include"])
 ],[

m4/ax_check_zlib.m4

@@ -119,7 +119,7 @@ then
     # If both library and header were found, action-if-found
     #
     m4_ifblank([$1],[
-		test "$enable_rpath" = yes && \
+		test "$enable_rpath" = yes -a "$ZLIB_HOME" != /usr && \
 		    LDFLAGS="$LDFLAGS -R${ZLIB_HOME}/lib"
                 LIBS="-lz $LIBS"
                 AC_DEFINE([HAVE_LIBZ], [1],

m4/ax_lib_expat.m4

@@ -181,7 +181,7 @@ p = NULL;
                 [
                 EXPAT_LIBS="$expat_lib_flags"
 		EXPAT_LDFLAGS="$expat_ld_flags"
-		test "$enable_rpath" = yes && \
+		test "$enable_rpath" = yes -a "$expat_prefix" != /usr && \
 		    EXPAT_LDFLAGS="$EXPAT_LDFLAGS -R$expat_prefix/lib"
                 expat_lib_found="yes"
                 AC_MSG_RESULT([found])

m4/lftp_lib_readline.m4

@@ -183,7 +183,7 @@ rl_completion_matches(0,0);
                 [
                 READLINE_LIBS="$readline_lib_flags"
 		READLINE_LDFLAGS="$readline_ld_flags"
-		test "$enable_rpath" = yes && \
+		test "$enable_rpath" = yes -a "$readline_prefix" != /usr && \
 		    READLINE_LDFLAGS="$READLINE_LDFLAGS -R$readline_prefix/lib"
                 readline_lib_found="yes"
                 AC_MSG_RESULT([found])

m4/ssl.m4

@@ -21,8 +21,7 @@ AC_CACHE_VAL(lftp_cv_openssl,
 		if test $found_loc != "none"; then
 			lftp_cv_openssl="OPENSSL_LIBS=\"-lssl -lcrypto\""
 			if test $found_loc != default; then
-				r=""
-				test "$enable_rpath" = yes && r=" -R$found_loc/lib"
+				r=""; test "$enable_rpath" = yes -a "$found_loc" != /usr && r=" -R$found_loc/lib"
 				lftp_cv_openssl="$lftp_cv_openssl OPENSSL_LDFLAGS=\"-L$found_loc/lib$r\""
 				lftp_cv_openssl="$lftp_cv_openssl OPENSSL_CPPFLAGS=-I$found_loc/include"
 			fi