Backport another libc++ patch for std::filesystem (and locale) usage

This fixes linking against a DLL of libc++ while using the common headers
(generated from the static version of the library, but which work for
both shared and static versions) when calling e.g. std::filesystem::u8path.

patches/llvm-project/0022-libcxx-Avoid-intermediate-string-objects-for-substri.patch

@@ -1,7 +1,7 @@
 From 497842a9ebb0ca1a6f871a07c0f4b4f1c700a798 Mon Sep 17 00:00:00 2001
 From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
 Date: Thu, 11 Mar 2021 13:06:08 +0200
-Subject: [PATCH 22/24] [libcxx] Avoid intermediate string objects for
+Subject: [PATCH 22/25] [libcxx] Avoid intermediate string objects for
  substrings in windows operator/=
 
 Check that appends with a path object doesn't do allocations, even