Make VPATH builds work again.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@4668 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/configure.in b/configure.in
index 0ef4311..96bfeb2 100644
--- a/configure.in
+++ b/configure.in
@@ -20,7 +20,7 @@
         [AC_MSG_ERROR([Directory '$withval' does not exist, or does not contain Vex])])
 ],
 [
-    VEX_DIR=`pwd`/VEX
+    VEX_DIR='$(top_srcdir)/VEX'
 ])
 AC_SUBST(VEX_DIR)