Index: test/builtins/CMakeLists.txt
===================================================================
--- test/builtins/CMakeLists.txt
+++ test/builtins/CMakeLists.txt
@@ -17,6 +17,11 @@
 if (NOT APPLE)
 foreach(arch ${BUILTIN_SUPPORTED_ARCH})
   set(BUILTINS_TEST_TARGET_ARCH ${arch})
+  if (WIN32 AND NOT MINGW AND NOT CYGWIN)
+    set(BUILTINS_STATIC_LIB_SUFFIX ".lib")
+  else()
+    set(BUILTINS_STATIC_LIB_SUFFIX ".a")
+  endif()
   string(TOLOWER "-${arch}-${OS_NAME}" BUILTINS_TEST_CONFIG_SUFFIX)
   get_test_cc_for_arch(${arch} BUILTINS_TEST_TARGET_CC BUILTINS_TEST_TARGET_CFLAGS)
   if (${arch} STREQUAL "armhf")
Index: test/builtins/Unit/lit.cfg
===================================================================
--- test/builtins/Unit/lit.cfg
+++ test/builtins/Unit/lit.cfg
@@ -24,8 +24,9 @@
 config.test_source_root = os.path.dirname(__file__)
 
 # Path to the static library
-base_lib = os.path.join(config.compiler_rt_libdir, "libclang_rt.builtins-%s.a "
-    % config.target_arch)
+suffix = get_required_attr(config, "builtins_lib_name_suffix")
+base_lib = os.path.join(config.compiler_rt_libdir, "libclang_rt.builtins-%s"
+    % config.target_arch) + suffix
 
 builtins_source_dir = os.path.join(
   get_required_attr(config, "compiler_rt_src_root"), "lib", "builtins")
Index: test/builtins/Unit/lit.site.cfg.in
===================================================================
--- test/builtins/Unit/lit.site.cfg.in
+++ test/builtins/Unit/lit.site.cfg.in
@@ -4,7 +4,7 @@
 config.builtins_lit_source_dir = "@BUILTINS_LIT_SOURCE_DIR@/Unit"
 config.target_cflags = "@BUILTINS_TEST_TARGET_CFLAGS@"
 config.target_arch = "@BUILTINS_TEST_TARGET_ARCH@"
-
+config.builtins_lib_name_suffix = "@BUILTINS_STATIC_LIB_SUFFIX@"
 # Load common config for all compiler-rt lit tests.
 lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/test/lit.common.configured")