soong: Use new linker file properties

So that dependencies are set up properly

Change-Id: I027eb0f69d85a8afb40b0bc30719ab47ea6c8874
diff --git a/Android.bp b/Android.bp
index 1364e46..81670e3 100644
--- a/Android.bp
+++ b/Android.bp
@@ -88,11 +88,9 @@
             },
         },
         darwin: {
-            ldflags: [
-                "-Wl,-unexported_symbols_list,${SrcDir}/external/libcxx/lib/libc++unexp.exp",
-                "-Wl,-force_symbols_not_weak_list,${SrcDir}/external/libcxx/lib/notweak.exp",
-                "-Wl,-force_symbols_weak_list,${SrcDir}/external/libcxx/lib/weak.exp",
-            ],
+            unexported_symbols_list: "lib/libc++unexp.exp",
+            force_symbols_not_weak_list: "lib/notweak.exp",
+            force_symbols_weak_list: "lib/weak.exp",
         },
 
         linux: {