From Zixing Liu:

d/p/fix-unwind-detection-logic.patch: use an upstream patch to fix libunwind detection logic when compiler-rt is disabled.

debian/changelog

@@ -1,3 +1,11 @@
+llvm-toolchain-16 (1:16.0.6-22) UNRELEASED; urgency=medium
+
+  [ Zixing Liu ]
+  * d/p/fix-unwind-detection-logic.patch: use an upstream patch to fix
+    libunwind detection logic when compiler-rt is disabled.
+
+ -- Gianfranco Costamagna <locutusofborg@debian.org>  Wed, 06 Mar 2024 08:38:53 +0100
+
 llvm-toolchain-16 (1:16.0.6-21) unstable; urgency=medium
 
   [ Steve Langasek ]

debian/patches/fix-unwind-detection-logic.patch

@@ -0,0 +1,39 @@
+From 7c5e4e5fa3a948fc662be3a6bf057021d32f72e6 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
+Date: Thu, 5 Oct 2023 11:41:11 +0300
+Subject: [PATCH] Reapply [compiler-rt] Check for and use -lunwind when linking
+ with -nodefaultlibs (#66584)
+
+If libc++ is available and should be used as the ubsan C++ ABI library,
+the check for libc++ might fail if libc++ is a static library, as the
+-nodefaultlibs flag inhibits a potential compiler default -lunwind.
+
+Just like the -nodefaultlibs configuration tests for and manually adds a
+bunch of compiler default libraries, look for -lunwind too.
+
+This is a reland of #65912.
+---
+ compiler-rt/cmake/config-ix.cmake | 10 ++++++++++
+ 1 file changed, 10 insertions(+)
+
+diff --git a/compiler-rt/cmake/config-ix.cmake b/compiler-rt/cmake/config-ix.cmake
+index 09a9b62ce4cd37..a8e078f1ebc988 100644
+--- a/compiler-rt/cmake/config-ix.cmake
++++ b/compiler-rt/cmake/config-ix.cmake
+@@ -63,6 +63,16 @@ if (C_SUPPORTS_NODEFAULTLIBS_FLAG)
+                         moldname mingwex msvcrt)
+     list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
+   endif()
++  if (NOT TARGET unwind)
++    # Don't check for a library named unwind, if there's a target with that name within
++    # the same build.
++    check_library_exists(unwind _Unwind_GetRegionStart "" COMPILER_RT_HAS_LIBUNWIND)
++    if (COMPILER_RT_HAS_LIBUNWIND)
++      # If we're omitting default libraries, we might need to manually link in libunwind.
++      # This can affect whether we detect a statically linked libc++ correctly.
++      list(APPEND CMAKE_REQUIRED_LIBRARIES unwind)
++    endif()
++  endif()
+ endif ()
+ 
+ # CodeGen options.

debian/patches/series

@@ -135,7 +135,7 @@ protobuf_3.21.patch
 # compiler-rt
 compiler-rt/compilerrt-builtins-arch-fix-armhf.diff
 compiler-rt/compilerrt-build-scudo-standalone-option.diff
-
+fix-unwind-detection-logic.patch
 
 # wasm patches
 wasm/wasm-ld-path.diff