Store decoded SILK pulses as 16-bit vector

This saves 640 bytes on the peak stack usage.
Moves deemphasis() call out of celt_decode_lost() to reduce peak stack
Adds SMALL_FOOTPRINT hack to the CELT PLC too
Delaying allocation of the SILK temporary output buffer to reduce peak stack
Moves CELT PLC pitch search to a separate function to reduce peak stack
Don't allocate pulses on the stack when calling the SILK PLC.

Also minor C89 fix for the previous commit
Another aliasing hack in the SILK PLC with SMALL_FOOTPRINT
Fixes SMALL_FOOTPRINT for float
Preventing unnecessary stack use when using a large decode buffer

This was causing pseudostack builds to fail because opus_demo uses a 2-second
buffer.
Minor refactoring of the SILK PLC code to save more stack
pseudostack instrumentation (off by default)
Fixes the decode_fec case for b76888d

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
Add tests/test_ to Makefile.unix.
Fix declaration after statement in fixed point.