Fix bionic-unit-tests-glibc

Also add another test for dlsym(RTLD_NEXT, ..)

Bug: http://b/33106624
Test: run bionic-unit-tests-glibc and bionic-unit-tests
Change-Id: I340165d66bf2360b0e3273d3561a08cb5e7bd025
diff --git a/tests/Android.bp b/tests/Android.bp
index 3e1e13b..688d8e1 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -476,7 +476,10 @@
 
     include_dirs: ["bionic/libc"],
 
-    ldflags: ["-Wl,--export-dynamic"],
+    ldflags: [
+        "-Wl,--rpath,${ORIGIN}/../bionic-loader-test-libs",
+        "-Wl,--export-dynamic",
+    ],
 
     sanitize: {
         never: false,