Conditional include directories

[Mike Gran]

Hello all,

In a standalone project makefile I want to add a -I directory
parameter to a CFLAGS variable.

On a 32-bit box, I need to add it as
-I/stage2/lib/dbus-1.0/include
 
One a 64-bit box, I need to add it as
-I/stage2/lib64/dbus-1.0/include 

There are a bunch of ways to do this, I guess.  I could
check to see if the /stage2/lib64 directory exists.  I could
somehow check if the box is 32-bit or 64-bit.
 
What's easiest (in a readability / maintainability sense)?
 
Thanks,
 
Mike Gran