xdiff: move stdint.h to xdiff.h It's more correct to put it in xdiff.h since that file actually uses int64_t etc and xdiff.h is included by xinclude.h. This should fix the oss-fuzz build. Thanks durin42 for discovering the issue. Test Plan: `make local` and xdiff related tests still work. Differential Revision: https://phab.mercurial-scm.org/D2848