<limits> must be explicitly included when compiling with with gcc 11.

diff --git a/llvm/utils/benchmark/src/benchmark_register.h b/llvm/utils/benchmark/src/benchmark_register.h
index 0705e219f2fa..4caa5ad4da07 100644
--- a/llvm/utils/benchmark/src/benchmark_register.h
+++ b/llvm/utils/benchmark/src/benchmark_register.h
@@ -1,6 +1,7 @@
 #ifndef BENCHMARK_REGISTER_H
 #define BENCHMARK_REGISTER_H
 
+#include <limits>
 #include <vector>
 
 #include "check.h"
