Enable MOZ_OPUS_FIXED inside the opus makefile if
MOZ_SAMPLE_TYPE_FLOAT32 is not defined. This is the
general proxy for floating point audio support in
other areas of the code.
We could have defined MOZ_OPUS_FIXED directly in
the configure script (and still could) but I liked
this better.
This builds the opus reference library in media/libopus.
We support both fixed and floating point builds, switched
by MOZ_OPUS_FIXED. Currently this isn't defined by anything
but should probably offer a configure option, and default
to true on arm.
Thanks to Tim Terriberry for additional review.