[native_toolchain_c] Tool resolver caching

[dcharkes]

Currently, the tool resolving logic has no caching, this means that tools that are resolved relative to another tool trigger a re-resolving of that tool.

This makes tool resolving slower than needed.

However, addressing this for normal use is low priority. We'd likely only look up a single compiler and potentially an archiver per invocation of a build.dart.

A possible way to address this would be to have a ToolsCache that can be threaded through the code like the Logger.