Fix a few more warnings by Clang.

- Apple Clang 17.0.0.
- png, z, jpeg lib integer cast warnings remain
- FLTK callback function cast warnings remain.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/threads.cxx b/test/threads.cxx
index 9c6f768f6..4c8a94d11 100644
--- a/test/threads.cxx
+++ b/test/threads.cxx
@@ -97,7 +97,7 @@ extern "C" void* prime_func(void* p) {
   // initialize alternate buffers (struct prime) to store primes
 
   struct prime pr[2];
-  pr[0].idx       = pr[1].idx       = n/2 - 1;
+  pr[0].idx       = pr[1].idx       = ((int)n/2 - 1);
   pr[0].done      = 0;
   pr[1].done      = 1;
   pr[0].terminal  = pr[1].terminal  = terminal;