From 01fe12a053c29735af87f9ba78746bb0cdf79abd Mon Sep 17 00:00:00 2001
From: Eric Fiselier <eric@efcs.ca>
Date: Wed, 16 Jan 2019 02:16:57 +0000
Subject: Attempt to make test_macros.h even more minimal

---
 libcxx/test/support/test_macros.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/libcxx/test/support/test_macros.h b/libcxx/test/support/test_macros.h
index 2813d1ff068..e4525353417 100644
--- a/libcxx/test/support/test_macros.h
+++ b/libcxx/test/support/test_macros.h
@@ -11,7 +11,18 @@
 #ifndef SUPPORT_TEST_MACROS_HPP
 #define SUPPORT_TEST_MACROS_HPP
 
-#include <ciso646> // Get STL specific macros like _LIBCPP_VERSION
+// Attempt to get STL specific macros like _LIBCPP_VERSION using the most
+// minimal header possible. If we're testing libc++, we should use `<__config>`.
+// If <__config> isn't available, fall back to <ciso646>.
+#ifdef __has_include
+# if __has_include("<__config>")
+#   include <__config>
+#   define TEST_IMP_INCLUDED_HEADER
+# endif
+#endif
+#ifndef TEST_IMP_INCLUDED_HEADER
+#include <ciso646>
+#endif
 
 #if defined(__GNUC__)
 #pragma GCC diagnostic push
-- 
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