Add test mapping to run the libunwind tests.

Created a special target, libunwindstack_unit_test, that doesn't
include the test that dlopen's a shared library. It appears atest
doesn't understand how to handle the require keyword.

Also, move the shared library into the libunwindstack_test directory
itself.

Test: Ran atest libunwindstack_unit_test.
Change-Id: I967919b1d74a08669b61d0363d80861685725609
diff --git a/libunwindstack/tests/LocalUnwinderTest.cpp b/libunwindstack/tests/LocalUnwinderTest.cpp
index 56a18cd..9936f7a 100644
--- a/libunwindstack/tests/LocalUnwinderTest.cpp
+++ b/libunwindstack/tests/LocalUnwinderTest.cpp
@@ -170,10 +170,10 @@
 
   std::string testlib(testing::internal::GetArgvs()[0]);
   auto const value = testlib.find_last_of('/');
-  if (value == std::string::npos) {
-    testlib = "../";
+  if (value != std::string::npos) {
+    testlib = testlib.substr(0, value + 1);
   } else {
-    testlib = testlib.substr(0, value + 1) + "../";
+    testlib = "";
   }
   testlib += "libunwindstack_local.so";