build: Enable AC_SYS_LARGEFILE
build: Enable AC_SYS_LARGEFILE

This results in `_LARGE_FILES` and related macros in config.h, which are
now applied to all of our source files. In particular, this fixes large
file support for ws certificate scanning.

Fixes #16778

martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit