Tweak to allow the use of this Makefile with the ICC compiler.
Patch by Gregory Czajkowski <gregczajkowski@yahoo.com>.
Related to BZ #339542.


git-svn-id: svn://svn.valgrind.org/vex/trunk@2980 8f6e269a-dfd6-0310-a8e1-e2731360e62c