Windows builds failing for master

Release and Debug builds, both 32bit and 64bit, have the same issue 64bit:

(Link target) -> 
  libisc.def : error LNK2001: unresolved external symbol isc_string_strlcat [c:\cygwin64\home\jenkins\workspace\bind9-master-win2012-x64-vs2017\lib\isc\win32\libisc.vcxproj]
  libisc.def : error LNK2001: unresolved external symbol isc_string_strlcpy [c:\cygwin64\home\jenkins\workspace\bind9-master-win2012-x64-vs2017\lib\isc\win32\libisc.vcxproj]
  .\Debug\libisc.lib : fatal error LNK1120: 2 unresolved externals [c:\cygwin64\home\jenkins\workspace\bind9-master-win2012-x64-vs2017\lib\isc\win32\libisc.vcxproj]

    49 Warning(s)
    3 Error(s)

last successful build was at 3949450f, first failing build was at e860375d