avcodec: Use av_reallocp where suitable

Signed-off-by: Martin Storsjö <martin@martin.st>
configure: detect Solaris libc

Add preprocessor flags for API availability as necessary.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
configure: Prefix libc-related variables with "libc_"

Simplifies host/target libc detection splitting.
avframe: add codec-independent stereoscopic metadata
h264: parse frame packing arrangement SEI messages and save relevant stereo3d information
libx264: set frame packing information when relevant information is found
mpeg12dec: parse frame packing arrangement user_data and save relevant stereo3d information
mpeg12enc: set frame packing information when relevant metadata is found
hevc: parse frame packing arrangement SEI messages and save relevant stereo3d information