GCC 4.6.0 kernel compile failure and -Werror=unused-but-set-variable

[bradfa]

When building kernels with GCC 4.6.0 the new way GCC deals with -Werror and unused-but-set-variable is slightly different than on GCC 4.5. Now, kernel compiles that set but don't use variables in a whole bunch of places will cause the make to fail. That's nice of GCC to point out these types of warnings and the kernel Makefile wants these warnings, but we don't really want the make to stop because of them.

See -dev mailing list thread finding this on a MIPS build:  http://lists.cross-lfs.org/pipermail/clfs-dev-cross-lfs.org/2011-April/000941.html

LKML also found this on PowerPC:  https://lkml.org/lkml/2011/3/9/229

The proposed workaround is some sed'ing but there might be kernel patches in the works as well to simply fix this. Best would be to fix the offending source files so the warnings don't come up in the first place and keep -Werror but I'm not a kernel hacker (at least not yet).