RFR: 8339336: Fix build system whitespace to adhere to coding conventions

[Magnus Ihse Bursie]

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. 

I have made a single type of change per commit in this branch. It might be easier to review this by looking at one commit at a time.

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Commit messages:
 - Multi-line lists should have \ on the last line and end with #
 - Make ### delimiters consistent length
 - Setup* calls should end with )) on a separate line
 - Trailing \ should be preceded by space
 - Comma should be followed by space, unless not possible
 - Assignments in Makefiles should be surrounded by space

Changes: https://git.openjdk.org/jdk/pull/20798/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20798&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339336
  Stats: 636 lines in 81 files changed: 27 ins; 10 del; 599 mod
  Patch: https://git.openjdk.org/jdk/pull/20798.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20798/head:pull/20798

PR: https://git.openjdk.org/jdk/pull/20798