Fix editors/openoffice-4 build with clang 6.0.0 by compiling with
-std=gnu++98 since that was the default for the compilers historically
used for the build. It turns out that -std=c++98 does not work
because the vigra headers depend on LLONG_MAX and friends, which
are not defined without the GNU extensions.

Compensate for a recent poudriere change by overriding $HOME and
setting it to /tmp if $HOME is not writeable. Some of the test
code run during the build wants to use mkstemp() to create temporary
directories under $HOME, which does not work for the "nobody" user
which points $HOME at /nonexistent.

No PORTREVISION bump since this is a build fix and there is no
change to the package.

PR: 225129
Reported by: jbeich