Fix build

tests/perfmodels/regression_based_01.c

@@ -46,7 +46,7 @@ void memset_cpu(void *descr[], void *arg)
 	unsigned n = STARPU_VECTOR_GET_NX(descr[0]);
 	unsigned i;
 
-	usleep(1000);
+	starpu_usleep(1000);
 
 	for (i=0; i<n ; i++)
 	{

tests/perfmodels/regression_based_02.c

@@ -43,7 +43,7 @@ void memset0_cpu(void *descr[], void *arg)
 	unsigned n = STARPU_VECTOR_GET_NX(descr[0]);
 	unsigned i;
 
-	usleep(100);
+	starpu_usleep(100);
 
 	for (i=0; i<n ; i++)
 	{

tests/perfmodels/regression_based_03.c

@@ -44,7 +44,7 @@ void memset0_cpu(void *descr[], void *arg)
 	unsigned n = STARPU_VECTOR_GET_NX(descr[0]);
 	unsigned i;
 
-	usleep(100);
+	starpu_usleep(100);
 
 	for (i=0; i<n ; i++)
 	{