graphics/librsvg2-rust: fix build on big-endian

patch-vendor_crossbeam-* patches are necessary on powerpc. They may be removed
after Rust 1.56.0 is released, upstream for crossbeam* crates regenerates
no_atomic.rs and those changes flow into ports.

Same for the patch for builtns.rs (except that it also affects powerpc64le
which is already in the upstream cfg_expr crate, but powerpc has not yet landed
there).

To fix build generally on big-endian (so powerpc and powerpc64 at the moment),
merging https://gitlab.gnome.org/GNOME/librsvg/-/commit/92df18a3faf80c1d6d35899d9a5d22c74adfb8f8
is also necessary.