uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

pkgs/development/compilers/mrustc/patches/0001-use-shared-llvm.patch

@@ -0,0 +1,12 @@
+--- a/rustc-1.29.0-src/src/librustc_llvm/lib.rs
+--- b/rustc-1.29.0-src/src/librustc_llvm/lib.rs
+@@ -23,6 +23,9 @@
+ #![feature(link_args)]
+ #![feature(static_nobundle)]
+ 
++// https://github.com/rust-lang/rust/issues/34486
++#[link(name = "ffi")] extern {}
++
+ // See librustc_cratesio_shim/Cargo.toml for a comment explaining this.
+ #[allow(unused_extern_crates)]
+ extern crate rustc_cratesio_shim;