This fixes token pasting, making it expand when
it should expand, and paste before expansion when
it should paste before expanding.
#define CAT(a, b) a ## b
#define BAR 3
#define FOO CAT(BAR, 3)
FOO
now produces 33, while
#define CAT(a, b) a ## b
#define EOF (-1)
#define NOP(x) x
NOP(CAT(foo, EOF))
CAT(,EOF)
CAT(,)
produces
fooEOF
(-1)
<empty>
respectively.
37b86df09f