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>

libswresample/Makefile

@@ -8,6 +8,7 @@ HEADERS = swresample.h                       \
 
 OBJS = audioconvert.o                        \
        dither.o                              \
+       log2_tab.o                            \
        rematrix.o                            \
        resample.o                            \
        swresample.o                          \

libswresample/log2_tab.c

+#include "libavutil/log2_tab.c"