Do define SAL_DLLEXTENSION properly for iOS, too

Do it even if it can never be used successfully in an iOS app anyway,
as they are not supposed to load dynamic libraries (except system
ones).

sal/inc/sal/config.h

@@ -97,8 +97,14 @@
 
 #ifdef IOS
 #define SAL_UNX
-#define SAL_DLLEXTENSION
+/* SAL_DLLEXTENSION should not really be used on iOS, as iOS apps are
+ * not allowed to load own dynamic libraries.
+ */
+#define SAL_DLLEXTENSION ".dylib"
 #define SAL_DLLPREFIX "lib"
+/* This is fairly pointless too, an iOS app consists of a single
+ * executable (plus data files).
+ */
 #define SAL_PRGEXTENSION ".bin"
 #define SAL_PATHSEPARATOR ':'
 #define SAL_PATHDELIMITER '/'