Protect use of pthread functions with #ifdef HAVE_PTHREAD_H.

loader/kthread.c

diff --git a/loader/kthread.c b/loader/kthread.c
index 48d7c4a..f27b3de 100644
--- a/loader/kthread.c
+++ b/loader/kthread.c
@@ -392,7 +392,7 @@
  * If they are not available, the libc defaults to
  * non-threadsafe operation (not good). */
 
-#if defined(__GLIBC__) || defined(__FreeBSD__)
+#if defined(HAVE_PTHREAD_H) && (defined(__GLIBC__) || defined(__FreeBSD__))
 
 /* adapt as necessary (a construct like this is used in glibc sources) */
 #define strong_alias(orig, alias) \
@@ -1010,4 +1010,4 @@
     _pthread_cleanup_pop           /* ptr__pthread_cleanup_pop */
 };
 
-#endif /* __GLIBC__ || __FREEBSD__ */
+#endif /* HAVE_PTHREAD_H && (__GLIBC__ || __FREEBSD__) */