Fix #line syntax checks (PR 39647)

[Chris Lattner]

On Apr 18, 2009, at 8:29 AM, Joseph S. Myers wrote:

> This patch fixes PR 39647, a preprocessor bug where #line directives
> failed to allow for macros expanding to nothing after the initial line
> number and file name.
>
> Bootstrapped with no regressions on x86_64-unknown-linux-gnu.  Applied
> to mainline.

Does this patch permit:

#define EMPTY
#include <limits.h> EMPTY
#include "limits.h" EMPTY

?  If not, I think that's a bug (at least in c99)

-Chris