Removed list mangling

[NOhs]

Regarding #74, this merge request removes most occurences of set where we might want to preserve the order. Compile flags for sure need the order preserved. For the include paths I think it shouldn't be advertised, but for debugging purposes it is better if the include paths are in a somewhat reasonable order.

[codecov]

Codecov Report

Merging #80 into master will decrease coverage by 1.76%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master      #80      +/-   ##
==========================================
- Coverage      81%   79.23%   -1.77%     
==========================================
  Files          12       12              
  Lines         979      992      +13     
==========================================
- Hits          793      786       -7     
- Misses        186      206      +20

Impacted Files	Coverage Δ
clang_build/target.py	89.76% <100%> (-0.16%)	⬇️
clang_build/io_tools.py	93.4% <100%> (-6.6%)	⬇️
clang_build/project.py	72.47% <66.66%> (+0.64%)	⬆️
clang_build/platform.py	68.18% <0%> (-29.55%)	⬇️
clang_build/clang_build.py	68.98% <0%> (+0.33%)	⬆️

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[NOhs]

This should be ready for merging now.

[NOhs]

I think the OSX CI is still broken, it reports everything runs fine, but it is missing in the coverage report I think.

[GPMueller]

To be honest I don't quite understand how the Travis tests are running through if Python 3.7 really is a requirement, since on the Linux VMs, only Python 3.6 is available:

clang-build/.travis.yml

Lines 8 to 11 in 890b0a6

	- language: python
	os: linux
	env: DEPLOY=true
	python: 3.6

Changing it to 3.7 is apparently not possible yet.

[NOhs]

I'll merge for now, while we look for a way to support OSX CI in the future.