Fix coqdoc test-suite target on Windows.
Fix coqdoc test-suite target on Windows.

Commit 8f12597 introduced new output tests but these were broken on Windows.
We fix them by using --strip-trailing-cr option of diff, like in other
output tests in the test-suite.

SkySkimmer/coq,maximedenes/coq,ejgallego/coq,ppedrot/coq,ejgallego/coq,silene/coq,JasonGross/coq,JasonGross/coq,Matafou/coq,silene/coq,silene/coq,letouzey/coq-wip,SkySkimmer/coq,coq/coq,gares/coq,SkySkimmer/coq,maximedenes/coq,coq/coq,ejgallego/coq,gares/coq,ppedrot/coq,Matafou/coq,ppedrot/coq,Zimmi48/coq,gares/coq,ppedrot/coq,letouzey/coq-wip,ppedrot/coq,ejgallego/coq,letouzey/coq-wip,Matafou/coq,maximedenes/coq,SkySkimmer/coq,Zimmi48/coq,coq/coq,letouzey/coq-wip,Zimmi48/coq,gares/coq,gares/coq,maximedenes/coq,Zimmi48/coq,coq/coq,JasonGross/coq,maximedenes/coq,JasonGross/coq,letouzey/coq-wip