This adds the OSS audio backend, which is basically a slightly modified
version of core/oslib/alsa_audiostream.cpp from the skmp/linux-x64
branch (as of commit cdf9f3dc971506c2efd979275c2869f064e1027c).
The ALSA backend will be included during compilation if HOST_OS is OS_LINUX
and neither TARGET_NACL32 nor ANDROID are defined. This should be
changed to a USE_ALSA flag in the future (for constistency and and
simplicity reasons), but i didn't want to put too much stuff into this
commit.
Jan Holthuis