[PATCH] elf: Fix tests that rely on ld.so.cache for cross-compiling

[DJ Delorie]

Patch looks good to me as-is but I'll note a few other options in case
we like those better :-)

* could put "ldconfig" in the scriptlet instead of a file, esp if it
  needs to be run in a specific order wrt installing other dso's, like
  if it needs to be run *before* corrupting a dso.

* the test case could just run ldconfig itself if it knows it's testing
  it.

* test-container could look for a zero-length etc/ld.so.cache in the
  test.root as a trigger to run ldconfig