build: check if AS supports the '.func' directive

Not supported by Clang's integrated assembler. Since it just adds
debug information it can safely omitted.
oggenc: Support flushing the muxer

This allows the caller to write all buffered data to disk, allowing
the caller to know at what byte position in the file a certain
packet starts (any packet written after the flush will be located
after that byte position).

Signed-off-by: Martin Storsjö <martin@martin.st>
Merge commit 'd5a55981986ac5d1a31aef3a8d16eaff8534a412'

* commit 'd5a55981986ac5d1a31aef3a8d16eaff8534a412':
  build: check if AS supports the '.func' directive

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '95b7fa1729b93bbb3f4fb85a5c0cb53cf970c3c7'

* commit '95b7fa1729b93bbb3f4fb85a5c0cb53cf970c3c7':
  oggenc: Support flushing the muxer

Conflicts:
	libavformat/version.h

Merged-by: Michael Niedermayer <michaelni@gmx.at>
huffyuvdec: implement trick

When the joint table does not contain a valid entry, the decoding restarts
from scratch. By implementing the trick of jumping to the 2nd level of the
individual table (and inlining the whole), a speed improvement of 5-10%
is possible.

On a 1000-frames YUV4:2:0 video, before:
362851 decicycles in 422, 262094 runs, 50 skips
182488 decicycles in gray, 262087 runs, 57 skips
Object size: 23584
Overall time: 8.377

After:
346800 decicycles in 422, 262079 runs, 65 skips
168197 decicycles in gray, 262077 runs, 67 skips
Object size: 23188
Overall time: 7.878

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>