libc++: enable frame apis in libunwind.

The bootstrapping hack used by the rust package on clang subsystems
(namely, substituting compiler-rt and libunwind for libgcc and using the
official gcc-based binaries to bootstrap) attempts to link to
__register_frame_info and __deregister_frame_info on i686.  Enabling
this option brings them back.

Author: jeremyd2019

mingw-w64-libc++/PKGBUILD

@@ -12,7 +12,7 @@ _version=18.1.2
 _rc=""
 _tag=llvmorg-${_version}${_rc}
 pkgver=${_version}${_rc/-/}
-pkgrel=1
+pkgrel=2
 arch=(any)
 mingw_arch=('mingw32' 'mingw64' 'ucrt64' 'clang64' 'clang32' 'clangarm64')
 url="https://libcxx.llvm.org/"
@@ -119,6 +119,7 @@ build() {
     -DLIBCXXABI_ENABLE_SHARED=OFF \
     -DLIBCXXABI_ENABLE_STATIC=ON \
     -DLIBCXXABI_HAS_WIN32_THREAD_API=ON \
+    -DLIBUNWIND_ENABLE_FRAME_APIS=ON \
     -DLIBUNWIND_ENABLE_SHARED=ON \
     -DLIBUNWIND_ENABLE_STATIC=ON \
     "${_extra_config[@]}" \