Revert "Stop checking for duplicate basenames"

This reverts commit 540e4b1e665aa4a69c89906abf267904b571f87b.

Slightly updated to comment/target at libtool, rather than Mac make/MSVC08.

See https://codereview.chromium.org/670063006/#msg11
and https://code.google.com/p/gyp/issues/detail?id=384.

R=thakis@chromium.org
BUG=gyp:384

Review URL: https://codereview.chromium.org/1151963003
6 files changed