Generate the longest error message in C++
19 characters

Create a file a.cpp with this content :  

#include __FILE__
p;


Compile as :   

g++ a.cpp


and get amazing 21300 lines error messages  :  

In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1,


...

... 21280 error lines ...
...  

In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0,
                 from a.cpp:1,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0,
                 from a.cpp:1:
a.cpp:2:1: error: ‘p’ does not name a type
In file included from a.cpp:1:0:
a.cpp:2:1: error: ‘p’ does not name a type
a.cpp:2:1: error: ‘p’ does not name a type