[LLVMdev] make check-lit + grep escape characters

[Stepan Dyatkovskiy]

Hi all. I found that if you want to use grep with escape characters in 
lit, you should pass it within the double slash (\\). Since the first 
one is captured by python scripts and the second one by grep.
E.g. if you want to capture "grep icmp ule" you should pass
"grep icmp\\ ule"

So I'm going to commit the test with strings like this. How stable this 
feature in lit?

-Stepan.