Use LIBRSVG_LIBS, LIBM to satisfy dependencies of RUST_LIB
Use LIBRSVG_LIBS, LIBM to satisfy dependencies of RUST_LIB

Otherwise linking with -Wl,--as-needed fails.

Signed-off-by: Simon McVittie <0e1aea601907c1a85c2dc96e5ea37e23c58d2e9b@debian.org>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg