[llvm-rc] Handle Windows line endings in tag-html test (#113000)
The tag-html.test has been failing for me and [in
CI](https://buildkite.com/llvm-project/github-pull-requests/builds/111277#0192a122-c5c9-4e4e-bc5b-7532fec99ae4)
if Git happens to decide to check out the baseline file with Windows
line endings.
This fix for this is to call `tr` to strip Windows newlines when copying
the baselines files to the test output directory before embedding them.