Revert "Update aosp/master libcxx rebase to r263688"

The world is burning.

This reverts commit c004fd909c006eec55077c52ee119e1fa338c9e9, reversing
changes made to 1418e4163da4bb0b9e3fe496e51c23a0dce399d9.
diff --git a/include/cstring b/include/cstring
index d550695..d60b992 100644
--- a/include/cstring
+++ b/include/cstring
@@ -78,13 +78,30 @@
 using ::strncmp;
 using ::strcoll;
 using ::strxfrm;
+
 using ::memchr;
+
 using ::strchr;
+
 using ::strcspn;
+
 using ::strpbrk;
+
 using ::strrchr;
+
 using ::strspn;
+
 using ::strstr;
+
+// MSVCRT, GNU libc and its derivates already have the correct prototype in <string.h> #ifdef __cplusplus
+#if !defined(__GLIBC__) && !defined(_LIBCPP_MSVCRT) && !defined(__sun__) && !defined(_STRING_H_CPLUSPLUS_98_CONFORMANCE_)
+inline _LIBCPP_INLINE_VISIBILITY       char* strchr(      char* __s, int __c) {return ::strchr(__s, __c);}
+inline _LIBCPP_INLINE_VISIBILITY       char* strpbrk(      char* __s1, const char* __s2) {return ::strpbrk(__s1, __s2);}
+inline _LIBCPP_INLINE_VISIBILITY       char* strrchr(      char* __s, int __c) {return ::strrchr(__s, __c);}
+inline _LIBCPP_INLINE_VISIBILITY       void* memchr(      void* __s, int __c, size_t __n) {return ::memchr(__s, __c, __n);}
+inline _LIBCPP_INLINE_VISIBILITY       char* strstr(      char* __s1, const char* __s2) {return ::strstr(__s1, __s2);}
+#endif
+
 #ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 using ::strtok;
 #endif