Add Windows line-ending support when parsing Perforce conflict marker.
This fixes 2 tests for Bug 35187 (https://bugs.llvm.org/show_bug.cgi?id=35187).
@zturner According to https://llvm.org/docs/GettingStarted.html#software, we shouldn't be relying on dos2unix nor unix2dos to be present on a build machine.
Note that the $'string' syntax (ANSI-C quotes) is a bash extension. According to the page mentioned above, the LLVM builds should only be relying on having a Bourne shell (sh). But, are there still any *nix system out there where /bin/sh isn't a link for \bin\bash ? I.e. Is relying on bash+sed fine here ?
A fully portable solution would be to write python scripts for dos2unix.py and unix2dos.py. That way, one would not be relying on build tools that LLVM isn't already using.
Any advice on how to proceed ?