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/0025-libcxx-Make-the-visibility-attributes-consistent-for.patch

@@ -0,0 +1,98 @@
+From 138e1609764e2226938df8cd6176303b41e4f325 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
+Date: Tue, 18 May 2021 14:45:08 +0000
+Subject: [PATCH 25/25] [libcxx] Make the visibility attributes consistent for
+ __narrow_to_utf8/__widen_from_utf8
+
+Use the same visiblity attributes as for all other template
+specializations in the same file; declare the specialization itself
+using _LIBCPP_TYPE_VIS, and don't use _LIBCPP_EXPORTED_FROM_ABI on
+the destructor. Methods that are excluded from the ABI are marked
+with _LIBCPP_INLINE_VISIBILITY.
+
+This makes the vtable exported from DLL builds of libc++. Practically,
+it doesn't make any difference for the CI configuration, but it
+can make a difference in mingw setups.
+
+Differential Revision: https://reviews.llvm.org/D102717
+
+(cherry picked from commit 3a6be27978aa3e83e9dc2ff2402b2569ce0686fd)
+---
+ libcxx/include/__locale | 16 ++++++++--------
+ 1 file changed, 8 insertions(+), 8 deletions(-)
+
+diff --git a/libcxx/include/__locale b/libcxx/include/__locale
+index 77e5faab2676..c2800e88e8d2 100644
+--- a/libcxx/include/__locale
++++ b/libcxx/include/__locale
+@@ -1484,14 +1484,14 @@ struct __narrow_to_utf8<8>
+ 
+ _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+ template <>
+-struct _LIBCPP_TEMPLATE_VIS __narrow_to_utf8<16>
++struct _LIBCPP_TYPE_VIS __narrow_to_utf8<16>
+     : public codecvt<char16_t, char, mbstate_t>
+ {
+     _LIBCPP_INLINE_VISIBILITY
+     __narrow_to_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
+ _LIBCPP_SUPPRESS_DEPRECATED_POP
+ 
+-    _LIBCPP_EXPORTED_FROM_ABI ~__narrow_to_utf8();
++    ~__narrow_to_utf8();
+ 
+     template <class _OutputIterator, class _CharT>
+     _LIBCPP_INLINE_VISIBILITY
+@@ -1520,14 +1520,14 @@ _LIBCPP_SUPPRESS_DEPRECATED_POP
+ 
+ _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+ template <>
+-struct _LIBCPP_TEMPLATE_VIS __narrow_to_utf8<32>
++struct _LIBCPP_TYPE_VIS __narrow_to_utf8<32>
+     : public codecvt<char32_t, char, mbstate_t>
+ {
+     _LIBCPP_INLINE_VISIBILITY
+     __narrow_to_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
+ _LIBCPP_SUPPRESS_DEPRECATED_POP
+ 
+-    _LIBCPP_EXPORTED_FROM_ABI ~__narrow_to_utf8();
++    ~__narrow_to_utf8();
+ 
+     template <class _OutputIterator, class _CharT>
+     _LIBCPP_INLINE_VISIBILITY
+@@ -1578,14 +1578,14 @@ struct __widen_from_utf8<8>
+ 
+ _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+ template <>
+-struct _LIBCPP_TEMPLATE_VIS __widen_from_utf8<16>
++struct _LIBCPP_TYPE_VIS __widen_from_utf8<16>
+     : public codecvt<char16_t, char, mbstate_t>
+ {
+     _LIBCPP_INLINE_VISIBILITY
+     __widen_from_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
+ _LIBCPP_SUPPRESS_DEPRECATED_POP
+ 
+-    _LIBCPP_EXPORTED_FROM_ABI ~__widen_from_utf8();
++    ~__widen_from_utf8();
+ 
+     template <class _OutputIterator>
+     _LIBCPP_INLINE_VISIBILITY
+@@ -1614,14 +1614,14 @@ _LIBCPP_SUPPRESS_DEPRECATED_POP
+ 
+ _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+ template <>
+-struct _LIBCPP_TEMPLATE_VIS __widen_from_utf8<32>
++struct _LIBCPP_TYPE_VIS __widen_from_utf8<32>
+     : public codecvt<char32_t, char, mbstate_t>
+ {
+     _LIBCPP_INLINE_VISIBILITY
+     __widen_from_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
+ _LIBCPP_SUPPRESS_DEPRECATED_POP
+ 
+-    _LIBCPP_EXPORTED_FROM_ABI ~__widen_from_utf8();
++    ~__widen_from_utf8();
+ 
+     template <class _OutputIterator>
+     _LIBCPP_INLINE_VISIBILITY
+-- 
+2.25.1
+