8a/a.h:
. Removed <u.h> and <libc.h> includes as they work better in "a.y".
. Made definition of EOF conditional as it's defined in the Plan 9
  header files, but not elsewhere.

8a/a.y:
. Added <u.h> and <libc.h> because <stdio.h> in Plan 9 needs them.
  Sequence <u.h>, <stdio.h>, <libc.h> recommended by RSC.

8a/lex.c:
. Added <u.h> and <libc.h> as now needed by "a.h".
. Dropped <ctype.h>.

cc/lexbody:
. exit() -> exits().
. Dropped unwanted incrementation.

cc/macbody:
. Adjusted a few format specifications.

R=rsc
CC=golang-dev
https://golang.org/cl/4644047