Improve the OSVERSION==UNAME_r validation from r369644 by skipping it
if OSVERSION is specified on the cmdline. This makes testing simpler.

This only works for bmake.

1. make -V CONFIGURE_LIBS

-lnew_release

1. make -V CONFIGURE_LIBS OSVERSION=800000

-lolder_release

1. env OSVERSION=800000 make -V CONFIGURE_LIBS

make: "/root/svn/ports/Mk/bsd.port.mk" line 1182: UNAME_r (11.0-CURRENT) and OSVERSION (800000) do not agree on major version number.

1. echo OSVERSION=800000 >> /etc/make.conf
2. make -V CONFIGURE_LIBS

make: "/root/svn/ports/Mk/bsd.port.mk" line 1182: UNAME_r (11.0-CURRENT) and OSVERSION (800000) do not agree on major version number.

Reported by: danfe
With hat: portmgr