Make these ports (TenDRA, egcs, gcc28, glibstdc++28 and guavac, all
under lang) use ${OSREL} as defined in bsd.port.mk rev 1.281 and
1.227.2.43.

Note gcc28 is hopelessly broken, it uses an undefined variable
${GNUOSREL} and thus has an empty string wherever ${OSREL} should
be. However, it's consistent with its own PLIST at the current state
so I haven't "fixed" it yet.