Failure to build with LLVM for the Wii

[Link Mauve <linkmauve@linkmauve.fr>]

Hi,

I’m trying to build the kernel for the Nintendo Wii, using LLVM instead
of gcc, in order to bring Rust support to this architecture (and also
because my distribution doesn’t ship a cross-compiling gcc), but I get
this build issue near the end:
```
% make O=wii LLVM=1 ARCH=powerpc -j1
make[1]: Entering directory '/home/linkmauve/dev/linux/wii'
  GEN     Makefile
  CALL    ../scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  WRAP    arch/powerpc/boot/dtbImage.wii
objcopy: Unable to recognise the format of the input file `vmlinux'
make[3]: *** [../arch/powerpc/boot/Makefile:394: arch/powerpc/boot/dtbImage.wii] Error 1
make[2]: *** [../arch/powerpc/Makefile:236: zImage] Error 2
make[1]: *** [/home/linkmauve/dev/linux/Makefile:248: __sub-make] Error 2
make[1]: Leaving directory '/home/linkmauve/dev/linux/wii'
make: *** [Makefile:248: __sub-make] Error 2
```

I believe it should use $(OBJCOPY) instead of objcopy, which is set to
llvm-objcopy, but couldn’t figure out where it is misconfigured.

Thanks for your help!

-- 
Link Mauve