[PATCH v2] gdb, include: replace pragmas with DIAGNOSTIC macros, fix build with g++ 4.8

[Simon Marchi]

>> Because of the POP, the diagnostic should go back to being disabled,
>> since it was disabled in the beginning, but that's now what we see
> 
> now -> not typo
> 
> Otherwise, LGTM.

Fixed and pushed, thanks.

Simon