This function is quite small (96B with GCC 11.2 on x64 Ubuntu 21.10
at -O3), making it more economical to duplicate it into libavformat
instead of exporting it as avpriv: Doing so saves 2x24B in .dynsim,
2x16B in .dynstr, 2x2B .gnu.version, 24B in .rela.plt, 16B in .plt,
16B in .plt.sec (if enabled), 4B .gnu.hash; besides the actual
duplicated code this also adds 2x8B .eh_frame_hdr and 24B .eh_frame.

In other words: Duplicating is neutral size-wise (it is also presumed
neutral for other systems). Given that it avoids the runtime
overhead of dynamic symbols, it is advantageouos to duplicate the
function.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>