Remove warnings from google-benchmarks in libcxx

[Eugene.Zelenko]

Committed in rL284179.

libcxx/benchmarks/ContainerBenchmarks.hpp

 #ifndef BENCHMARK_CONTAINER_BENCHMARKS_HPP
 #define BENCHMARK_CONTAINER_BENCHMARKS_HPP
 
 #include <cassert>
 
 #include "benchmark/benchmark_api.h"
 
 namespace ContainerBenchmarks {
 
 
 template <class Container, class GenInputs>
 void BM_ConstructIterIter(benchmark::State& st, Container, GenInputs gen) {
     auto in = gen(st.range(0));
+    const auto begin = in.begin();
     const auto end = in.end();
     benchmark::DoNotOptimize(&in);
     while (st.KeepRunning()) {
-        Container c(in.begin(), in.end());
+        Container c(begin, end);
         benchmark::DoNotOptimize(c.data());
     }
 }
 
 template <class Container, class GenInputs>
 void BM_InsertValue(benchmark::State& st, Container c, GenInputs gen) {
     auto in = gen(st.range(0));
     const auto end = in.end();

libcxx/benchmarks/GenerateInput.hpp

 
 inline std::vector<std::string> getDuplicateStringInputs(size_t N) {
     std::vector<std::string> inputs(N, getRandomString(1024));
     return inputs;
 }
 
 inline std::vector<std::string> getRandomStringInputs(size_t N) {
     std::vector<std::string> inputs;
-    for (int i=0; i < N; ++i) {
+    for (size_t i=0; i < N; ++i) {
         inputs.push_back(getRandomString(1024));
     }
     return inputs;
 }
 
 inline std::vector<std::string> getSortedStringInputs(size_t N) {
     std::vector<std::string> inputs = getRandomStringInputs(N);
     std::sort(inputs.begin(), inputs.end());