[libcxxabi][CMake] Set --unwindlib=none when using LLVM libunwind

We already link libunwind explicitly so avoid trying to link toolchain's
default libunwind which may be missing. This matches what we already do
for libcxx.

Differential Revision: https://reviews.llvm.org/D129469

diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index a8c79aa6f380a451012b082160cd35b142009ce3..248acc6567ab91bfdde217bc17699346b12092c8 100644 (file)
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -99,6 +99,13 @@ else()
   add_link_flags_if_supported(-nodefaultlibs)
 endif()
 
+if (CXX_SUPPORTS_UNWINDLIB_EQ_NONE_FLAG AND LIBCXXABI_USE_LLVM_UNWINDER)
+  # If we're linking directly against the libunwind that we're building
+  # in the same invocation, don't try to link in the toolchain's
+  # default libunwind (which may be missing still).
+  add_link_flags_if_supported(--unwindlib=none)
+endif()
+
 if ( APPLE )
   if (LLVM_USE_SANITIZER)
     if (("${LLVM_USE_SANITIZER}" STREQUAL "Address") OR