gcc-based Windows buildfarm animals are not happy about a multiline
regular expression I added recently.  Try to accomodate; existing
pg_basebackup tests suggest that \n should work instead of a bare
newline, but throw in \r also.  This being perl, TIMTOWTDI.
Also remove the pointless $ at the end of the pattern, for extra luck.

(If this doesn't work, I'll probably just split the regex in two.)

Per buildfarm members jacana and fairywren.

Discussion: https://postgr.es/m/3562.1576161217@sss.pgh.pa.us