Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/limits.h

@@ -1,5 +1,5 @@
 // -*- C++ -*-
-//===--------------------------- limits.h ---------------------------------===//
+//===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -37,12 +37,35 @@ Macros:
 
 */
 
-#include "third_party/libcxx/__config"
+#include <__config>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#pragma GCC system_header
+#  pragma GCC system_header
 #endif
 
-#include "libc/isystem/limits.h"
+#ifdef _LIBCPP_COMPILER_GCC
+
+// GCC header limits.h recursively includes itself through another header called
+// syslimits.h for some reason. This setup breaks down if we directly
+// #include_next GCC's limits.h (reasons not entirely clear to me).
+// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107795 for more details.
+// Therefore, we manually re-create the necessary include sequence below:
+
+// Get the system limits.h defines (force recurse into the next level)
+#define _GCC_LIMITS_H_
+#define _GCC_NEXT_LIMITS_H
+#include_next <limits.h>
+
+// Get the ISO C defines
+#undef _GCC_LIMITS_H_
+#include_next <limits.h>
+
+#else
+
+#  if __has_include_next(<limits.h>)
+#    include_next <limits.h>
+#  endif
+
+#endif // _LIBCPP_COMPILER_GCC
 
 #endif // _LIBCPP_LIMITS_H