Add a quote character to the sed command to cause it to be quoted.
Hopefully, which will help both gnuwin and MSys versions of sed tokenize
the command line the same way.
The escaped parens seem to confuse the combination of lit, cygwin
quoting, and cygwin's sed. unxutils sed in cmd.exe is fine with both
forms, so use the extended regex form that doesn't need an escaped
paren.
llvm-svn: 374753