Fixes fixed-point on x86 (no SSE).
Drop the stdint size tests that we never use anywhere

These were probably cribbed from libogg, but we don't use them here,
opus_types.h instead has a list of hardcoded arch definitions.
Moves VBR calculations to a separate function.

Does not change the behaviour of the VBR code in most cases. The only
exception is that the VBR offset is now taken into accound in the base_rate,
which will have a (very minor) impact on CVBR at low rate.
Adds a quick hack to replace the normal calls with the multistream version.
Fixes stupid tf calibration bugs introduced/exposed in f77410d
SSE optimization of remove_doubling()

Should be trivial to adapt for Neon.
Splits cwrsi() inner loop in two to avoid the min/max and some load chains
Further optimization to cwrsi()

Makes it possible to skip the first loop in some cases.