In preparation to update QuakeForge to the latest version, unbreak, stagify,
and clean up the port beforehand:

• Require compiler that supports nested functions
• Do not enable extra compiler optimizations by default; they're known to be the cause of sporadic build and run-time failures
• Make snd_oss actually work: mmap()ped buffer for the DMAing into /dev/dsp was set up incorrectly. FreeBSD always requires MAP_SHARED for device mappings
• Remove vestiges of Tier-2 (sparc64) and dropped (alpha) arch gimmicks
• Define LICENSE (GPLv2), miscellaneous cleanups
• Transfer maintainership to games@ while here as well

Submitted by: kib (sound fix)