llvmPackages_11.libcxxabi: More precise libunwind inclusion

pkgs/development/compilers/llvm/11/libcxxabi/default.nix

@@ -1,7 +1,7 @@
 { lib, stdenv, llvm_meta, cmake, fetch, libcxx, libunwind, llvm, version
+, enableShared ? !stdenv.hostPlatform.isStatic
 , standalone ? stdenv.hostPlatform.useLLVM or false
 , withLibunwind ? !stdenv.isDarwin && !stdenv.isFreeBSD && !stdenv.hostPlatform.isWasm
-, enableShared ? !stdenv.hostPlatform.isStatic
 }:
 
 stdenv.mkDerivation {
@@ -35,6 +35,7 @@ stdenv.mkDerivation {
 
   cmakeFlags = lib.optionals standalone [
     "-DLLVM_ENABLE_LIBCXX=ON"
+  ] ++ lib.optionals (standalone && withLibunwind) [
     "-DLIBCXXABI_USE_LLVM_UNWINDER=ON"
   ] ++ lib.optionals stdenv.hostPlatform.isWasm [
     "-DLIBCXXABI_ENABLE_THREADS=OFF"