swresample: include ff_log2_tab for shared builds

swresample: include ff_log2_tab for shared builds

This is done in accordance with all other libraries, which no longer access ff_log2_tab from avutil directly for shared builds, and instead obtain their own copy.

This change is required for MSVC DLL builds, as well as avoids accessing a private symbol from another library.

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