Build our benchmarks against glibc too.

Bug: 18556607
Change-Id: I455ac8b93c0835836180e549486bc52d393ee6a6
diff --git a/benchmarks/pthread_benchmark.cpp b/benchmarks/pthread_benchmark.cpp
index 11db56d..92e5998 100644
--- a/benchmarks/pthread_benchmark.cpp
+++ b/benchmarks/pthread_benchmark.cpp
@@ -80,7 +80,7 @@
 
 static void BM_pthread_mutex_lock_ERRORCHECK(int iters) {
   StopBenchmarkTiming();
-  pthread_mutex_t mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER;
+  pthread_mutex_t mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
   StartBenchmarkTiming();
 
   for (int i = 0; i < iters; ++i) {
@@ -94,7 +94,7 @@
 
 static void BM_pthread_mutex_lock_RECURSIVE(int iters) {
   StopBenchmarkTiming();
-  pthread_mutex_t mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
+  pthread_mutex_t mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
   StartBenchmarkTiming();
 
   for (int i = 0; i < iters; ++i) {