There are probably simpler examples, but the X10DT project at https://x10.svn.sf.net/svnroot/x10/courses/trunk/SC2011Tutorial/GLB shows the problem.
In order to get the link stage to work for the UTS application, I had to copy the contents of sha1.c into UTS_SHA1Rand.cc. When compiling under X10DT, sha1.o is never built, and therefore the functions in it are missing from libGLB.a, which causes the linking to fail.
To reproduce the bug, edit UTS_SHA1Rand.cc and remove all the code below the /****** HACK ****/ comment.
It builds with the command line compiler without this hack, so it is some bad interaction or bug in how X10DT is dealing with post compilation.