Out of tree build. Partial fix for Bug 333628.

Patch by Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>.
Partial fix. make && make check now works with builddir != srcdir.
But make regtest doesn't yet.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13949 a5019735-40e9-0310-863c-91ae7b9d1cf9