compile.c, gc.c: suppress warnings

* compile.c (iseq_compile_each): suppress implicit conversion
  warning by old apple gcc 4.2.

* gc.c (RVALUE_FLAGS_AGE, heap_page_allocate): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47580 b2dd03c8-39d4-4d8f-98ff-823fe69b080e