Minimize the changes in #5277

Instead of including `mruby/presym.h` everywhere, we provided the
fallback `mruby/presym.inc` under `include/mruby` directory, and specify
`-I<build-dir>/include` before `-I<top-dir>/include` in `presym.rake`.
So even when someone drops `-I<build-dir>/include` in compiler options,
it just compiles without failure.

mrbgems/mruby-array-ext/src/array.c

@@ -3,7 +3,6 @@
 #include <mruby/array.h>
 #include <mruby/range.h>
 #include <mruby/hash.h>
-#include <mruby/presym.h>
 
 /*
  *  call-seq: