glibc: add missing pthread_spin_{init,destroy}

h/t Sebastian Wicki for the bug report.

glibc/sysdeps/riscv/nptl/pthread_spin_destroy.c

@@ -20,11 +20,13 @@
 #include "pthreadP.h"
 
 
-#ifndef __riscv_atomic
 int
-pthread_spin_destroy (lock)
-     pthread_spinlock_t *lock;
+pthread_spin_destroy (pthread_spinlock_t *lock)
 {
+#ifdef __riscv_atomic
+  /* Nothing to do.  */
+  return 0;
+#else
   return pthread_mutex_destroy(lock);
-}
 #endif
+}

glibc/sysdeps/riscv/nptl/pthread_spin_init.c

@@ -21,10 +21,13 @@
 #include "pthreadP.h"
 
 
-#ifndef __riscv_atomic
 int
 pthread_spin_init (pthread_spinlock_t *lock, int pshared)
 {
+#ifdef __riscv_atomic
+  *lock = 0;
+  return 0;
+#else
   return pthread_mutex_init(lock, NULL);
-}
 #endif
+}