C++ cpp lineno breakage

[Mike Stump]

Hey, Matt, Zack, did you break:

char *p = "\q"; /* { dg-error "unknown escape" } */
int i;

this recently for C++?  The problem is the line numbers for cpp_error 
come out as the last line number in the source file.  In the above, we 
currently see:

t.cc:2:1: warning: unknown escape sequence '\q'

instead of:

t.cc:1:11: warning: unknown escape sequence '\q'

(which is what we see in C).