Unavailable symbols in libwebp Wrapper

[stemann]

Some symbols are not available in the JLL binary (the shared object), which may cause errors when trying to call these:

julia> pic_pointer = Ptr{WebP.WebPPicture}()

julia> WebP.Wrapper.WebPPictureInit(pic_pointer)
ERROR: could not load symbol "WebPPictureInit":
/home/user/.julia/artifacts/b0dd47a5c6466709af32a1dfd76d973073ec07e6/lib/libwebp.so: undefined symbol: WebPPictureInit

This is likely due to the definitions being marked with WEBP_INLINE rather than WEBP_EXTERN, e.g. in https://github.com/webmproject/libwebp/blob/v1.4.0/src/webp/encode.h#L369-L378 , in a combination with the build script in https://github.com/JuliaPackaging/Yggdrasil/blob/master/L/libwebp/build_tarballs.jl