Link libc++.a against libc++abi.a

The libcxx build system is supposed to do this, but this broke
for system-libcxxabi with the switch to object library targets.
It's not obvious how to best fix this in the build system, so
for now manually merge the archives using an mri script.

libcxx.spec

@@ -9,7 +9,7 @@
 
 Name:		libcxx
 Version:	%{libcxx_version}%{?rc_ver:~rc%{rc_ver}}
-Release:	1%{?dist}
+Release:	2%{?dist}
 Summary:	C++ standard library targeting C++11
 License:	MIT or NCSA
 URL:		http://libcxx.llvm.org/
@@ -102,9 +102,21 @@ common_cmake_flags="\
 
 %cmake_build
 
-# Copy result libc++.a
+# Manually link libc++.a against libc++abi.a, because the libcxx build system is currently
+# broken when system-libcxxabi is used.
+# Also place libc++.a into results-static so we can install it later.
+LIBCXX_A=`find $PWD -name libc++.a`
 mkdir results-static
-find . -name libc++.a -exec cp {} ./results-static \;
+pushd results-static
+ar -M <<EOM
+CREATE libc++.a
+ADDLIB $LIBCXX_A
+ADDLIB %{_libdir}/libc++abi.a
+SAVE
+END
+EOM
+ranlib libc++.a
+popd
 
 %cmake  -GNinja \
 	$common_cmake_flags \
@@ -145,6 +157,9 @@ install -m 0644 src/include/*.h %{buildroot}%{_includedir}/libcxx-internal/
 
 
 %changelog
+* Tue Sep 13 2022 Nikita Popov <npopov@redhat.com> - 15.0.0-2
+- Link libc++.a against libc++abi.a
+
 * Thu Sep 08 2022 Nikita Popov <npopov@redhat.com> - 15.0.0-1
 - Update to LLVM 15.0.0