Re-hide mempcpy.

Bug: https://github.com/android/ndk/issues/2081
Test: vcpkg install --triplet arm64-android gettext-libintl
Change-Id: Id2eff76b929543f18d64accd5b6afb64bc63e117
diff --git a/libc/include/string.h b/libc/include/string.h
index 7c1c3be..873ea82 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -52,8 +52,12 @@
 int memcmp(const void* _Nonnull __lhs, const void* _Nonnull __rhs, size_t __n) __attribute_pure__;
 void* _Nonnull memcpy(void* _Nonnull, const void* _Nonnull, size_t);
 #if defined(__USE_GNU)
+// This conflicts with a polyfill in gettext-libintl
+// https://github.com/android/ndk/issues/2081
+#if __ANDROID_API__ >= 23
 void* _Nonnull mempcpy(void* _Nonnull __dst, const void* _Nonnull __src, size_t __n) __INTRODUCED_IN(23);
 #endif
+#endif
 void* _Nonnull memmove(void* _Nonnull __dst, const void* _Nonnull __src, size_t __n);
 
 /**