Index: libcxx/trunk/include/__config
===================================================================
--- libcxx/trunk/include/__config
+++ libcxx/trunk/include/__config
@@ -184,9 +184,11 @@
 // Need to detect which libc we're using if we're on Linux.
 #if defined(__linux__)
 #include <features.h>
-#if !defined(__GLIBC_PREREQ)
-#define __GLIBC_PREREQ(a, b) 0
-#endif // !defined(__GLIBC_PREREQ)
+#if defined(__GLIBC_PREREQ)
+#define _LIBCPP_GLIBC_PREREQ(a, b) __GLIBC_PREREQ(a, b)
+#else
+#define _LIBCPP_GLIBC_PREREQ(a, b) 0
+#endif // defined(__GLIBC_PREREQ)
 #endif // defined(__linux__)
 
 #ifdef __LITTLE_ENDIAN__
@@ -416,10 +418,10 @@
 #define _LIBCPP_HAS_C11_FEATURES
 #elif defined(__linux__)
 #if !defined(_LIBCPP_HAS_MUSL_LIBC)
-#if __GLIBC_PREREQ(2, 15) || defined(__BIONIC__)
+#if _LIBCPP_GLIBC_PREREQ(2, 15) || defined(__BIONIC__)
 #define _LIBCPP_HAS_QUICK_EXIT
 #endif
-#if __GLIBC_PREREQ(2, 17)
+#if _LIBCPP_GLIBC_PREREQ(2, 17)
 #define _LIBCPP_HAS_C11_FEATURES
 #endif
 #else // defined(_LIBCPP_HAS_MUSL_LIBC)