Bug 338681 Enable clone backtrace hack for i386-linux in helgrind.

glibc doesn't provide CFI unwind information right after the clone call
(because it would be invalid in the child). Enable the same workaround
for i386-linux that is already used for amd64-linux (subtract 3 from ip).

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14398 a5019735-40e9-0310-863c-91ae7b9d1cf9