#15965: Explicitly cast AT_FDCWD as (int).

Required on Solaris 10 (which defines AT_FDCWD as 0xffd19553),
harmless on other platforms.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 54f6cd2..e0efebf 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -414,7 +414,14 @@
 
 
 #ifdef AT_FDCWD
-#define DEFAULT_DIR_FD AT_FDCWD
+/*
+ * Why the (int) cast?  Solaris 10 defines AT_FDCWD as 0xffd19553 (-3041965);
+ * without the int cast, the value gets interpreted as uint (4291925331),
+ * which doesn't play nicely with all the initializer lines in this file that
+ * look like this:
+ *      int dir_fd = DEFAULT_DIR_FD;
+ */
+#define DEFAULT_DIR_FD (int)AT_FDCWD
 #else
 #define DEFAULT_DIR_FD (-100)
 #endif