Committed: old patch to btest-gcc.sh: Add libmudflap.sum, if it exists.

[Hans-Peter Nilsson]

I had a nagging feeling there was a patch I didn't commit.
Patch approval link, having link to the patch:
<http://gcc.gnu.org/ml/gcc-patches/2009-03/msg01509.html>
(modulo obvious adjustments to copyright line)

brgds, H-P