[libunwind] Revert "Use the from-scratch testing configuration by default"

This reverts commit 5a8ad80b6fa5cbad58b78384f534b78fca863e7f, which broke
the Bootstrapping build. I'm reverting until we've fixed the issue.

Differential Revision: https://reviews.llvm.org/D112082

GitOrigin-RevId: 070a2ddcb6657f1b497b8003384bae31e27e497d
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 93fd722..59d489b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -87,13 +87,7 @@
     "Additional linker flags for test programs.")
 set(LIBUNWIND_TEST_COMPILER_FLAGS "" CACHE STRING
     "Additional compiler flags for test programs.")
-
-if (LIBUNWIND_ENABLE_SHARED)
-  set(LIBUNWIND_DEFAULT_TEST_CONFIG "llvm-libunwind-shared.cfg.in")
-else()
-  set(LIBUNWIND_DEFAULT_TEST_CONFIG "llvm-libunwind-static.cfg.in")
-endif()
-set(LIBUNWIND_TEST_CONFIG "${LIBUNWIND_DEFAULT_TEST_CONFIG}" CACHE STRING
+set(LIBUNWIND_TEST_CONFIG "${CMAKE_CURRENT_SOURCE_DIR}/test/lit.site.cfg.in" CACHE STRING
   "The path to the Lit testing configuration to use when running the tests.
    If a relative path is provided, it is assumed to be relative to '<monorepo>/libunwind/test/configs'.")
 if (NOT IS_ABSOLUTE "${LIBUNWIND_TEST_CONFIG}")