Get gcc 4.7.4 to build

I'm failing to build the GCC 4.7.4 from live-bootstrap. The basic error is:

```plain
checking how to run the C++ preprocessor... /zb/store/hfwl0p2fzipd4aflhzgiajpaszz1s019-gcc-4.0.4/bin/cpp
configure: error: in `/build/src/gcc-4.7.4/build/gcc-4.7.4/build/libcpp':
configure: error: C++ preprocessor "/zb/store/hfwl0p2fzipd4aflhzgiajpaszz1s019-gcc-4.0.4/bin/cpp" fails sanity check
```