fix build of performance benchmarks

tools/run_tests/performance/build_performance.sh

@@ -53,7 +53,10 @@ do
     fi
     ;;
   "csharp")
-    python tools/run_tests/run_tests.py -l "$language" -c "$CONFIG" --build_only -j 8 --compiler coreclr
+    python tools/run_tests/run_tests.py -l "$language" -c "$CONFIG" --build_only -j 8
+    # unbreak subsequent make builds by restoring zconf.h (previously renamed by cmake portion of C#'s build)
+    # See https://github.com/grpc/grpc/issues/11581
+    (cd third_party/zlib; git checkout zconf.h)
     ;;
   "node"|"node_purejs")
     tools/run_tests/performance/build_performance_node.sh