* Don't build with "-march=native", because the generated binaries
won't work reliably on systems with a different CPU. Instead,
"--march=i686" is used on x86, and "--march=nocona" an x86_64.
Otherwise, "--march" remains unset.
* Compile with -O3 instead of -O2. This code is performance-critical.
* Don't build with '-g'.
svn path=/nixpkgs/trunk/; revision=22785
