[libc++/abi] Allow running back-deployment testing against libc++abi

Before this patch, we could only link against the back-deployment libc++abi
dylib. This patch allows linking against the just-built libc++abi, but
running against the back-deployment one -- just like we do for libc++.

Also, add XFAIL markup to flag expected errors.

Differential Revision: https://reviews.llvm.org/D91069

GitOrigin-RevId: 60ba1fefab927af64bc8a03958661bb8c1412684
diff --git a/test/libunwind/test/config.py b/test/libunwind/test/config.py
index 9231860..be2dcbd 100644
--- a/test/libunwind/test/config.py
+++ b/test/libunwind/test/config.py
@@ -17,7 +17,7 @@
         super(Configuration, self).__init__(lit_config, config)
         self.libunwind_src_root = None
         self.libunwind_obj_root = None
-        self.abi_library_path = None
+        self.abi_library_root = None
         self.libcxx_src_root = None
 
     def configure_src_root(self):
diff --git a/test/lit.site.cfg.in b/test/lit.site.cfg.in
index 8ff770f..cb2e087 100644
--- a/test/lit.site.cfg.in
+++ b/test/lit.site.cfg.in
@@ -7,7 +7,7 @@
 config.project_obj_root         = "@CMAKE_BINARY_DIR@"
 config.libunwind_src_root       = "@LIBUNWIND_SOURCE_DIR@"
 config.libunwind_obj_root       = "@LIBUNWIND_BINARY_DIR@"
-config.abi_library_path         = "@LIBUNWIND_LIBRARY_DIR@"
+config.abi_library_root         = "@LIBUNWIND_LIBRARY_DIR@"
 config.libcxx_src_root          = "@LIBUNWIND_LIBCXX_PATH@"
 config.libunwind_headers        = "@LIBUNWIND_SOURCE_DIR@/include"
 config.cxx_library_root         = "@LIBUNWIND_LIBCXX_LIBRARY_PATH@"