Thanks for your responses -- I did not receive notification of the same so could not respond earlier.
I do include a header irq.h in the board_setup.c file.
What you might want to do is expose some API to an upper layer routine which will have both of these libraries linked into it, and have THAT make the assignment. That's, at least, one way of solving this issue quickly.
When you say it has "both libraries linked into it", do you mean
a) a routine which has all the # include files from board_setup.c as well as irq.c?
b) a routine which calls functions from both these files?
Thanks again for your response,