[all-commits] [llvm/llvm-project] 317dc3: Reapply [runtimes] Fix building initial libunwind+...

[Martin Storsjö via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 317dc31e53b83c1d2a468d7a541925f0cc7d9dce
      https://github.com/llvm/llvm-project/commit/317dc31e53b83c1d2a468d7a541925f0cc7d9dce
  Author: Martin Storsjö <martin at martin.st>
  Date:   2021-12-08 (Wed, 08 Dec 2021)

  Changed paths:
    M libcxx/CMakeLists.txt
    M libcxx/cmake/config-ix.cmake
    M runtimes/CMakeLists.txt

  Log Message:
  -----------
  Reapply [runtimes] Fix building initial libunwind+libcxxabi+libcxx with compiler implied -lunwind

This does mostly the same as D112126, but for the runtimes cmake files.
Most of that is straightforward, but the interdependency between
libcxx and libunwind is tricky:

Libunwind is built at the same time as libcxx, but libunwind is not
installed yet. LIBCXXABI_USE_LLVM_UNWINDER makes libcxx link directly
against the just-built libunwind, but the compiler implicit -lunwind
isn't found. This patch avoids that by adding --unwindlib=none if
supported, if we are going to link explicitly against a newly built
unwinder anyway.

Reapplying this after
db32c4f45625dddc2c5cb683adf3d9cab7a9732f, which should fix the issues
that were reported last time this was applied.

Differential Revision: https://reviews.llvm.org/D113253