Hi Dave,

hmmm,

On my build machine:
$ /opt/cross/gcc-4.4.5-nolibc/x86_64-linux/bin/x86_64-linux-gcc -Wno-unused-but-set-variable -c -xc /dev/null -o /tmp/xx.o; echo $?
0
$ /opt/cross/gcc-4.4.5-nolibc/x86_64-linux/bin/x86_64-linux-gcc -Wunused-but-set-variable -c -xc /dev/null -o /tmp/xx.o; echo $?
cc1: error: unrecognized command line option "-Wunused-but-set-variable"
1
$ gcc -Wno-unused-but-set-variable -c -xc /dev/null -o /tmp/xx.o; echo $?
0
$ gcc -Wunused-but-set-variable -c -xc /dev/null -o /tmp/xx.o; echo $?
cc1: error: unrecognized command line option "-Wunused-but-set-variable"
1
$ gcc -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.5-8' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --with-arch-32=i586 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.5 (Debian 4.4.5-8) 

On master.kernel.org:

$ gcc -Wno-unused-but-set-variable -c -xc /dev/null -o /tmp/xx.o; echo $?
0
$ gcc -Wunused-but-set-variable -c -xc /dev/null -o /tmp/xx.o; echo $?
0
$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.4.5 20101112 (Red Hat 4.4.5-2) (GCC) 

-- 
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/