clar: don't use mkdtemp(3p) on SunOS

We do not have mkdtemp(3p) available on SunOS, as it has only been added
with POSIX.1-2008. Use the same compatibility code that we use on HP
NonStop, which falls back to using mktemp(3) plus mkdir(3).

clar/sandbox.h

@@ -128,7 +128,7 @@ static int build_sandbox_path(void)
 
 	if (mkdir(_clar_path, 0700) != 0)
 		return -1;
-#elif defined(__TANDEM)
+#elif defined(__sun) || defined(__TANDEM)
 	if (mktemp(_clar_path) == NULL)
 		return -1;