update_xiph_libs.sh: Install pdb files with libs.

Also silences warning related to EditAndContinue being enabled
for some configs (Dshow and MF builds use /SAFESEH, so
any use of EditAndContinue emits a warning).

BUG=https://code.google.com/p/webm/issues/detail?id=890

Change-Id: I7b350db0086e12ed9ef7e31d528a557f54bb1f8d