Port cleanup attribute to Oracle Studio 12.5

Port cleanup attribute to Oracle Studio 12.5

* INSTALL (--with-modules): List cleanup attribute as prereq.
* src/conf_post.h (__has_attribute_cleanup): Remove; no longer needed.
* src/emacs-module.c (MODULE_SETJMP_1): Don’t attempt to verify
(__has_attribute (cleanup)), as Oracle Studio 12.5 supports
__has_attribute only inside preprocessor expressions.  The C
compiler should check the cleanup attribute in the next line anyway.
(module_reset_handlerlist): Remove an unnecessary ‘const’
that causes Oracle Studio 12.5 to refuse to compile.