[CI] Add missing libunwind

Author: banach-space

.github/workflows/x86-ubuntu-llvm-from-sources.yml

@@ -36,7 +36,7 @@ jobs:
           cmake -G Ninja \
             -DCMAKE_BUILD_TYPE=Release \
             -DLLVM_ENABLE_PROJECTS="clang" \
-            -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+            -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
             -DLLVM_TARGETS_TO_BUILD="X86" \
             -DLLVM_OPTIMIZED_TABLEGEN=ON \
             ../llvm