ccache misses everything

[bates64]

This is because ccache doesn't cache when the input comes from stdin. We can fix this by either

1. calling gcc proper; or
2. piping cpp output to an intermediary .i file and then using the path of that file for cc1

instead of piping cpp into cc1 into as. We do this because we want to use modern cpp. To solve (1) maybe we can replace cpp in the gcc2.8.1 directory with a symlink to the modern cpp?

I prefer (1) because not invoking bash for every cc task will save build time.

Blocks #1151

[bates64]

For posterity this is fixed in dx because it just uses modern gcc for everything

[bates64]

To solve (1) maybe we can replace cpp in the gcc2.8.1 directory with a symlink to the modern cpp?

This may be trivial