Add short option fix for #3798, fix bug in test/SCONSFLAGS.py, fix space issue from #3436

[DeeeeLAN]

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt (and read the README.rst)
• I have updated the appropriate documentation
  • I don't think any documentation updates are necessary in this case.

[mwichmann]

This is nice work, got a lot further than my attempts to dig at this. Haven't had time to deep dive and/or think about the fiddling with SCons variables, but the evidence from the tests is promising. If this does go forward, someone will have to undo some of the doc warnings that were recently added to "don't do that" (nargs > 1, space separators). Also we should hunt down and tie in all the github issues that mention this problem, there are quite a few - at least the ones noted in #3436, there may be others too.

[bdbaddog]

Looks like test: test/AddOption/args-and-targets.py is failing?
Can you take a look and resolve?

[mwichmann]

So this test line:

test.run('-Q -q -x A TARG1', status=1, stdout="A\n\\['TARG1'\\]\n")

seems to indicate A is showing up in the targets at the point the SConstruct checks for it after all (one of the old problems this is trying to address), because if it does, then B is added to targets and the result indicates that's being seen:

STDOUT =========================================================================
2c2
< \['TARG1'\]
---
> ['TARG1', 'B']