compile time regressions (was: merging for 3.4)

[Benjamin Kosnik]

>  >   gcc-3.0.4/bin/g++    45.45 user
>  >   gcc-3.1.1/bin/g++    57.79 user  +27%
>  >   gcc-3.2.1/bin/g++    59.30 user  +30%
>  >   gcc-current/bin/g++  72.29 user  +59%

These indicate, to me, that the slowdown has nothing to do with
libstd++-v3. There just weren't substantial changes in the library
includes to cause this kind of slowdown between 3.0.x and 3.2.x.

It also indicates the PCH will be less and less useful unless the other
bits are brought back to normal. Depressing.

-benjamin