implement barrier attribute functions (essentially no-ops)

src/thread/pthread_barrierattr_destroy.c

@@ -0,0 +1,6 @@
+#include "pthread_impl.h"
+
+int pthread_barrierattr_destroy(pthread_barrierattr_t *a)
+{
+	return 0;
+}

src/thread/pthread_barrierattr_getpshared.c

@@ -0,0 +1,7 @@
+#include "pthread_impl.h"
+
+int pthread_barrierattr_getpshared(const pthread_barrierattr_t *a, int *pshared)
+{
+	*pshared = *a;
+	return 0;
+}

src/thread/pthread_barrierattr_init.c

@@ -0,0 +1,7 @@
+#include "pthread_impl.h"
+
+int pthread_barrierattr_init(pthread_barrierattr_t *a)
+{
+	memset(a, 0, sizeof *a);
+	return 0;
+}

src/thread/pthread_barrierattr_setpshared.c

@@ -0,0 +1,7 @@
+#include "pthread_impl.h"
+
+int pthread_barrierattr_setpshared(pthread_barrierattr_t *a, int pshared)
+{
+	*a = !!pshared;
+	return 0;
+}