testsuites/ada: Introduce init.c files

Provide an init.c for each Ada test instead of the #include <config.h>
magic which works only due to hand crafted include paths.

Update #3818.

testsuites/ada/support/initimpl.h

@@ -53,7 +53,7 @@ void check_type(long type, long size, long alignment);
 
 #define CONFIGURE_DISABLE_SMP_CONFIGURATION
 
-#include <config.h>
+#include <rtems/confdefs.h>
 
 const char rtems_test_name[] = ADA_TEST_NAME;