How to check as to in which file is a variable declared while debugging in gdb?

How to check as to in which file is a variable declared while debugging in
gdb?

I am going through code which is spread across multiple files. I have a
variable x which i am using in file A.c and its declared in B.h. I am
debugging using gdb under emacs. While in file A.c how do i check as to in
which file is my variable x declared?