K 10
svn:author
V 6
kevans
K 8
svn:date
V 27
2020-09-11T13:28:37.740731Z
K 7
svn:log
V 298
Only set WARNS if not defined

This would allow interested parties to do experimental runs with an
environment set appropriately to raise all the warnings throughout the
build; e.g. env WARNS=6 NO_WERROR=yes buildworld.

Not currently touching the numerous instances in ^/tools.

MFC after:	1 week

END