Fix build system whitespace to adhere to coding conventions

The build system code has unfortunately diverted in some places from the conventions as described in https://openjdk.org/groups/build/doc/code-conventions.html.

Instead of trying to fix these when touching code nearby, I'd like to make an effort to fix all issues at once and separately. Incremental fixes has their benefit, but they can also muddy the actual fix and are not always appreciated.

The updates in this patch have all been discovered using automated tools, but each and every change has been manually scrutinized. Those that the automatic tools pointed out that, but that were not obviously or clear-cut safe (e.g. adding spaces after comma, in `subst` or similar situations) were reverted before I pushed. I chose to err on the "First, do no harm" side, so there might be places that could have been corrected, but were not.