Add a kludge implementation of pthread_condattr_getclock

This function isn't optional, and in any case setclock *is* provided

expected/wasm32-wasip1-threads/defined-symbols.txt

@@ -1009,6 +1009,7 @@ pthread_cond_signal
 pthread_cond_timedwait
 pthread_cond_wait
 pthread_condattr_destroy
+pthread_condattr_getclock
 pthread_condattr_getpshared
 pthread_condattr_init
 pthread_condattr_setclock

libc-top-half/musl/src/thread/pthread_attr_get.c

@@ -1,5 +1,9 @@
 #include "pthread_impl.h"
 
+#ifndef __wasilibc_unmodified_upstream
+#include <common/clock.h>
+#endif
+
 int pthread_attr_getdetachstate(const pthread_attr_t *a, int *state)
 {
 	*state = a->_a_detach;
@@ -70,6 +74,15 @@ int pthread_condattr_getclock(const pthread_condattr_t *restrict a, clockid_t *r
 	*clk = a->__attr & 0x7fffffff;
 	return 0;
 }
+#else
+int pthread_condattr_getclock(const pthread_condattr_t *restrict a, clockid_t *restrict clk)
+{
+	if (a->__attr & 0x7fffffff == __WASI_CLOCKID_REALTIME)
+		*clk = CLOCK_REALTIME;
+	if (a->__attr & 0x7fffffff == __WASI_CLOCKID_MONOTONIC)
+		*clk = CLOCK_MONOTONIC;
+	return 0;
+}
 #endif
 
 int pthread_condattr_getpshared(const pthread_condattr_t *restrict a, int *restrict pshared)