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

This commit switches libunwind from using the complicated logic in
libc++'s testing configuration to a from-scratch configuration.
I tried to make sure that all cases that were handled in the old
config were handled by this one too, so hopefully this shouldn't
break anyone. However, if you encounter issues with this change,
please let me know and feel free to revert if I don't reply quickly.

This change was engineered to be easily revertable.

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

GitOrigin-RevId: 5a8ad80b6fa5cbad58b78384f534b78fca863e7f
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 59d489b..93fd722 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -87,7 +87,13 @@
     "Additional linker flags for test programs.")
 set(LIBUNWIND_TEST_COMPILER_FLAGS "" CACHE STRING
     "Additional compiler flags for test programs.")
-set(LIBUNWIND_TEST_CONFIG "${CMAKE_CURRENT_SOURCE_DIR}/test/lit.site.cfg.in" CACHE STRING
+
+if (LIBUNWIND_ENABLE_SHARED)
+  set(LIBUNWIND_DEFAULT_TEST_CONFIG "llvm-libunwind-shared.cfg.in")
+else()
+  set(LIBUNWIND_DEFAULT_TEST_CONFIG "llvm-libunwind-static.cfg.in")
+endif()
+set(LIBUNWIND_TEST_CONFIG "${LIBUNWIND_DEFAULT_TEST_CONFIG}" CACHE STRING
   "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}")