host-cargo: select host-rustc

host-cargo: select host-rustc

Buildroot documentation specifies that cargo-based package should only
depends on BR2_PACKAGE_HOST_RUSTC_ARCH_SUPPORTS and selects
BR2_PACKAGE_HOST_CARGO but this fails with the following error:

warning: (BR2_PACKAGE_LIBRSVG) selects BR2_PACKAGE_HOST_CARGO which has
unmet direct dependencies (BR2_PACKAGE_HAS_HOST_RUSTC)

Indeed, host-cargo depends on
BR2_PACKAGE_HAS_HOST_RUSTC which is selected only when host-rustc is
selected.

So instead of having to select both cargo and rustc in each cargo-based
package, replace BR2_PACKAGE_HAS_HOST_RUSTC dependency by
BR2_PACKAGE_HOST_RUSTC_ARCH_SUPPORTS and select
BR2_PACKAGE_HOST_RUSTC

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>