Phil's original path, after new Perl 5.20.2 was installed
C:\Perl64\site\bin;C:\Perl64\bin;C:\ProgramData\Oracle\Java\javapath;C:\Python34\;C:\Python34\Scripts;C:\Riverware\tools\Qt-485\bin;C:\Tcl\bin;C:\Perl\bin\;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\Diskeeper Corporation\Diskeeper;C:\RiverWare\bin;C:\RiverWare\bin.reorg;C:\RiverWare\tools\bin;C:\RiverWare\tools\tkcvs\bin;C:\RiverWare\tools\UnxUtils;%systemroot%\idmu\common;C:\Program Files (x86)\IBM\RationalPurifyPlus\Common;C:\Program Files (x86)\Rational\common;C:\Program Files\R\R-2.14.2\bin\x64;C:\PROGRA~1\DISKEE~1\DISKEE~1\;C:\Program Files (x86)\Common Files\Acronis\SnapAPI\;C:\Program Files (x86)\Acronis\CommandLineTool\;C:\Ruby193\bin

Modified path for Qt5 build
C:\Perl64\site\bin;C:\Perl64\bin;C:\ProgramData\Oracle\Java\javapath;C:\Python34\;C:\Python34\Scripts;C:\Tcl\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\Diskeeper Corporation\Diskeeper;C:\RiverWare\bin;C:\RiverWare\bin.reorg;C:\RiverWare\tools\bin;C:\RiverWare\tools\tkcvs\bin;%systemroot%\idmu\common;C:\Program Files (x86)\IBM\RationalPurifyPlus\Common;C:\Program Files (x86)\Rational\common;C:\Program Files\R\R-2.14.2\bin\x64;C:\PROGRA~1\DISKEE~1\DISKEE~1\;C:\Program Files (x86)\Common Files\Acronis\SnapAPI\;C:\Program Files (x86)\Acronis\CommandLineTool\;C:\Ruby193\bin;C:\Riverware\tools\icu-55.1\bin64;C:\Riverware\tools\Qt-542\gnuwin32\bin

Added built Qt5 bin:
C:\Riverware\tools\Qt-542\qtbase\bin;C:\Perl64\site\bin;C:\Perl64\bin;C:\ProgramData\Oracle\Java\javapath;C:\Python34\;C:\Python34\Scripts;C:\Tcl\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\Diskeeper Corporation\Diskeeper;C:\RiverWare\bin;C:\RiverWare\bin.reorg;C:\RiverWare\tools\bin;C:\RiverWare\tools\tkcvs\bin;%systemroot%\idmu\common;C:\Program Files (x86)\IBM\RationalPurifyPlus\Common;C:\Program Files (x86)\Rational\common;C:\Program Files\R\R-2.14.2\bin\x64;C:\PROGRA~1\DISKEE~1\DISKEE~1\;C:\Program Files (x86)\Common Files\Acronis\SnapAPI\;C:\Program Files (x86)\Acronis\CommandLineTool\;C:\Ruby193\bin;C:\Riverware\tools\icu-55.1\bin64;C:\Riverware\tools\Qt-542\gnuwin32\bin