codeparser: Compute extra cache components on the fly rather than later

codeparser: Compute extra cache components on the fly rather than later

In the initial implementation there was a relcutance on my part to
generate incremental cache components on the fly since it would lead
to some duplicate code.

We are now seeing problems where each thread reading in the saved cache
file causes significant overhead and can make the process appear to hang
on a many core build, particularly when the cache file is large.

This patch changes the code to maintain the delta in a separate dict
right from the start. The code duplication isn't too bad and could be
mitigated in other ways if it becomes an issue.

[YOCTO #2039 partial]

(Bitbake rev: cdd5d0dee6ab12326b252b6b505a316a52638cac)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>