Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -100,6 +100,10 @@
     "Specify C++ ABI library to use." FORCE)
 set_property(CACHE LIBCXX_CXX_ABI PROPERTY STRINGS ;${CXXABIS})
 
+# Build libc++abi with libunwind. We need this option to determine whether to
+# link with libunwind or libgcc_s while running the test cases.
+option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
+
 # TODO(ericwf): Remove these options by March/25/2015.
 # These CMake options have been removed in favor of a generic option
 # "LIBCXX_CXX_ABI_INCLUDE_PATHS". Issue an explicit error message explaining
Index: test/lit.site.cfg.in
===================================================================
--- test/lit.site.cfg.in
+++ test/lit.site.cfg.in
@@ -23,6 +23,7 @@
 config.generate_coverage        = "@LIBCXX_GENERATE_COVERAGE@"
 config.target_info              = "@LIBCXX_TARGET_INFO@"
 config.executor                 = "@LIBCXX_EXECUTOR@"
+config.llvm_unwinder            = "@LIBCXXABI_USE_LLVM_UNWINDER@"
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@LIBCXX_SOURCE_DIR@/test/lit.cfg")