build:wafsamba: refactored the gcc-based dependency calculation

[github at samba.org]

New comment by abartlet on Samba Github repository

https://github.com/samba-team/samba/pull/31#issuecomment-156891943
Comment:
I tried to look at these for review, but I'm also a bit lost in them.  I tend to accept ita's view with regard to build system patches. 

Can we get the cosmetics cleaned up and then I think obnoxxx and I can probably review them into Samba.