[PATH][Ada] Fix multilib handling of gnat.dg when RUNTESTFLAGS is used

[Eric Botcazou]

> It's commited on trunk and 4.4, testresults from the farm
> on x86_64 now use RUNTESTFLAGS for -m32/-m64:
>
> http://gcc.gnu.org/ml/gcc-testresults/2009-04/msg00689.html
> http://gcc.gnu.org/ml/gcc-testresults/2009-04/msg00696.html

Nice work!

-- 
Eric Botcazou