Fix write-region and its subroutines for buffers > 2GB.

Fix write-region and its subroutines for buffers > 2GB.

 src/fileio.c (a_write, e_write): Modify declaration of arguments and
 local variables to support buffers larger than 2GB.
 (Fcopy_file): Use EMACS_INT for return value of emacs_read.
 src/sysdep.c (emacs_write, emacs_read): Use ssize_t for last
 argument, local variables, and return value.
 src/lisp.h: Update prototypes of emacs_write and emacs_read.
 src/sound.c (vox_write): Use ssize_t for return value of emacs_write.