init: call pre_main before C++ constructors

This moves the platform specific initialization function pre_main
in front of C++ constructors. This is especially necessary for
platforms which need to setup the stack pointer (pre_main itself
is inline, hence no stack needed for this function).

lib/cm3/vector.c

@@ -74,6 +74,9 @@ void WEAK __attribute__ ((naked)) reset_handler(void)
 		*dest++ = 0;
 	}
 
+	/* might be provided by platform specific vector.c */
+	pre_main();
+
 	/* Constructors. */
 	for (fp = &__preinit_array_start; fp < &__preinit_array_end; fp++) {
 		(*fp)();
@@ -82,9 +85,6 @@ void WEAK __attribute__ ((naked)) reset_handler(void)
 		(*fp)();
 	}
 
-	/* might be provided by platform specific vector.c */
-	pre_main();
-
 	/* Call the application's entry point. */
 	main();