Fix building with gcc_target_rpath.

https://crrev.com/c/1459634 caused rpath_link to be set unconditionally,
but not used if gcc_target_rpath was set. This led to an "assignment had
no effect" error.

Change-Id: Ic5a2167391d49d008f78fa37fdd62bbaa3704eca
Reviewed-on: https://chromium-review.googlesource.com/c/1461354Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Erik Jensen <rkjnsn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630569}

build/config/gcc/BUILD.gn

@@ -65,11 +65,10 @@ config("symbol_visibility_default") {
 config("rpath_for_built_shared_libraries") {
   if (!is_android) {
     # Note: Android doesn't support rpath.
-    rpath_link = "."
     if (current_toolchain != default_toolchain || gcc_target_rpath == "") {
       ldflags = [
         # Want to pass "\$". GN will re-escape as required for ninja.
-        "-Wl,-rpath=\$ORIGIN/${rpath_link}",
+        "-Wl,-rpath=\$ORIGIN/.",
       ]
     } else {
       ldflags = [ "-Wl,-rpath=${gcc_target_rpath}" ]