[Buildroot] =?y?q?=5BBuildroot=5D=20=5BPATCH=201/4=5D=20package/rust=3A=20fix=20bootstrap=20with=20Rust=E2=89=A51=2E83?=

[El Mehdi YOUNES]

Patches 2 to 4 should be squashed into a single commit, as they logically belong together. 

I used multiple commits only for better clarity.