Fix compilation errors in 32-bit C++ mode on HP-UX 11/ia64. * m4/largefile.m4 (gl_SET_LARGEFILE_SOURCE): New macro. * modules/fseeko (configure.ac-early): Require it instead of AC_FUNC_FSEEKO. * modules/ftello (configure.ac-early): Likewise. * modules/fflush (configure.ac-early): Likewise.