I've noticed that after touching type.hpp in Valhalla, it requires more than 7 minutes to build hotspot. I would have suspected that we mostly recompile C2/opto source files. But that is far from the truth: A lot of unrelated source files must be recompiled, including, for example, C1, JFR, or runtime files.

In mainline, the impact is not that severe. But it still requires around 1 minute to build hotspot again on my machine after touching type.hpp. I've had a look at the include chains and removed quite a lot of unused includes and moved some code around where one include pulled in a lot of unnecessary code. The mainline patch could also be applied to the current Valhalla repository (with some small tweaks).

The results were quite promising. I could bring the compilation time significantly down in mainline and especially in Valhalla:
- Mainline: ~1min -> ~40s (1.5 times faster)
- Valhalla: ~7min -> ~40s (10.5 times faster)

I've only focused on type.hpp here but I guess other includes in the JIT compiler area or other parts of hotspot could also be improved to speed up recompilation after touching some header files.