redoconf: move -Wl,-rpath flags to shlib.rc and add -Wl,-z,origin.

It was kind of ugly to have this kind of special flag directly in
link.od; now we detect whether it's available.  This also gives a
project the ability to override the flag in some other way if they
want.

As a result, rc/shlib.rc needs to be included in all.rc.od if you want
to create or link against shared libraries.

While we're here, also add -Wl,-z,origin on platforms where it works.
This is apparently needed for FreeBSD 8.0 at least, and probably other
platforms.

Reported-by: Wayne Scott <wsc9tt@gmail.com>

docs/cookbook/c/all.rc.od

@@ -2,6 +2,7 @@
 rc_include \
 	rc/CC.required.rc \
 	rc/CXX.rc \
+	rc/shlib.rc \
 	rc/libqt4.rc \
 	rc/libgtk2.rc \
 	rc/Wextra.rc \

redoconf/link-shlib.od

@@ -1,5 +1,5 @@
 . ./redoconf.rc
-rc_include _all.rc rc/shlib.rc
+rc_include _all.rc
 
 # Tricky quoting: see _compile.od for details.
 if [ "$HAVE_SHLIB" = UNIX ]; then
@@ -40,6 +40,12 @@ elif [ "$HAVE_SHLIB" = MACOS ]; then
 		  \$LIBS
 	EOF
 else
+	if [ -z "$HAVE_SHLIB" ]; then
+		echo "link-shlib.od: fatal:" \
+			"must include rc/shlib.rc to use shared libraries." >&2
+		exit 90
+	fi
+
 	# If no shared library support and we try to build one,
 	# compensate by building a static library instead in the
 	# same place.

redoconf/link.od

@@ -13,7 +13,6 @@ cat >$3 <<-EOF
 	IFS="$NL"
 	set -f
 	\$LINK -o "\$o" \\
-	  -Wl,-rpath,'\$ORIGIN' \\
 	  \$LDFLAGS \$OPTFLAGS \\
 	  "\$@" \\
 	  \$LIBS

redoconf/rc/shlib.rc.od

@@ -27,17 +27,29 @@ try_macos_style() {
 
 if [ -n "$STATIC" ]; then
 	echo "--enable-static specified; not building shared libraries." >&2
-	rc_replaceln HAVE_SHLIB ""
+	rc_replaceln HAVE_SHLIB "STATIC"
 elif [ -n "$NOSHARED" ]; then
 	echo "--disable-shared specified; not building shared libraries." >&2
-	rc_replaceln HAVE_SHLIB ""
+	rc_replaceln HAVE_SHLIB "STATIC"
 elif try_unix_style; then
 	rc_replaceln HAVE_SHLIB UNIX
 elif try_macos_style; then
 	rc_replaceln HAVE_SHLIB MACOS
 else
 	echo "Not building shared libraries on this platform." >&2
-	rc_undo
+	rc_replaceln HAVE_SHLIB "STATIC"
-	rc_replaceln HAVE_SHLIB ""
 fi
+
+if [ "$HAVE_SHLIB" != "STATIC" ]; then
+	x='-Wl,-z,origin'
+	if (appendln LDFLAGS "$x" && rc_compile cc link); then
+		rc_appendln LDFLAGS "$x"
+	fi
+
+	x='-Wl,-rpath,$ORIGIN'
+	if (appendln LDFLAGS "$x" && rc_compile cc link); then
+		rc_appendln LDFLAGS "$x"
+	fi
+fi
+
 rc_save