Don't generate settings attribute when compiler flags are not specified

[marciniwanicki]

Resolves #414

BuildPhaseGenerator will not generate empty settings attribute for source PBXBuildFile elements when compiler flags are not specified.

Test Plan:

• Close Xcode
• Generate fixtures/ios_app_with_frameworks fixture
• Open generated .xcodeproj in a non-Xcode editor (i..e vim), ensure empty settings ={} attributes have not been generated

[tuistbot]

	1 Warning
⚠️	Have you introduced any user-facing changes? If so, please take some time to update the documentation. Keeping the documentation up to date makes it easier for users to learn how to use Tuist.

Generated by 🚫 Danger

[codecov]

Codecov Report

Merging #415 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #415      +/-   ##
=========================================
+ Coverage   92.29%   92.3%   +0.01%     
=========================================
  Files         293     293              
  Lines       15048   15071      +23     
=========================================
+ Hits        13888   13911      +23     
  Misses       1160    1160

Impacted Files	Coverage Δ
...atorTests/Generator/BuildPhaseGeneratorTests.swift	100% <100%> (ø)	⬆️
...TuistGenerator/Generator/BuildPhaseGenerator.swift	97.54% <100%> (+0.03%)	⬆️

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[ollieatkinson]

🗝

Looks good to me, I no longer see empty settings

[kwridan]

👍

[marciniwanicki]

Many thanks @ollieatkinson and @kwridan 🙌