mt_allocator.cc: Fix assumption that sizeof(void *) is equal to sizeof(size_t).

2014-11-14  Joel Sherrill <joel.sherrill@oarcorp.com>

	* src/c++98/mt_allocator.cc: Fix assumption that sizeof(void *) is
	equal to sizeof(size_t). The m32c breaks this assumption.

From-SVN: r217576