This script was trying to only rebuild the symbols when the binary
file was more recent than the symbols file. However, -nt fails when
the right hand side doesn't exist. Therefore it wouldn't actually dump
symbols and the sed script would fail later on.
This adds a test for the non-existance of the output file first.
TBR=mmoss
git-svn-id: http://src.chromium.org/svn/trunk/src/build@18659 4ff67af0-8c30-449e-8e8b-ad334ec8d88c