Add a test harness

Mostly cargo-culted from libcxxabi, since the unwinder was forked from there in
the first place. There may still be cruft that's only applicable to libcxxabi,
but that can be addressed in-tree.

https://reviews.llvm.org/D35038


git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@307266 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 032df56..68d90f6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -321,3 +321,5 @@
 if (LIBUNWIND_INCLUDE_DOCS)
   add_subdirectory(docs)
 endif()
+
+add_subdirectory(test)