Fix the build issues on mac for some samples (#358)

Fix the build issues on mac for basic/multi-module/multi-thread/
simple/spawn-thread/wasm-c-api under samples.
And all these samples could be run as expected.

Signed-off-by: Xiaokang Qin <xiaokang.qxk@antgroup.com>

core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c

@@ -2137,7 +2137,11 @@ static void convert_timestamp(
     struct timespec *out
 ) {
   // Store sub-second remainder.
+#ifndef __APPLE__
   out->tv_nsec = (__syscall_slong_t)(in % 1000000000);
+#else
+  out->tv_nsec = (long)(in % 1000000000);
+#endif
   in /= 1000000000;
 
   // Clamp to the maximum in case it would overflow our system's time_t.