[SR-9216] Don't honor SDKROOT in interpreter mode

[belkadan]

Previous ID	SR-9216
Radar	rdar://problem/21819253
Original Reporter	@belkadan
Type	Bug

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug, Driver, StarterBug
Assignee	Jon (JIRA)
Priority	Medium

md5: f3641cf6b439af1689bb8109248eccef

Issue Description:

People have tried to use Swift in Xcode Run Script build phases, but because Swift looks at the SDKROOT environment variable, the Run Script phase will fail when building a non-macOS target:

<unknown>:0: warning: using sysroot for 'iPhoneOS' but targeting 'MacOSX'
<unknown>:0: error: unable to load standard library for target 'x86_64-apple-macosx10.14'

We should just ignore SDKROOT when running the interpreter. Swift knows how to invoke xcrun to find the right SDK when it's not passed one explicitly.

[belkadan]

This would pretty much just be switching the two if branches dealing with SDKROOT in Driver.cpp, and then modifying the existing tests that exercise the SDKROOT behavior to make sure they cover this case.

[AnnaZaks]

Jon (JIRA User) Are you still fixing it or should we re-assign to someone else?

Thanks!

[Jeehut]

@AnnaZaks Did you get an answer from Jon (JIRA User) on the state of this? This is still an issue holding off Swift based command line tools of being usable in build scripts, like I reported on swift-sh here:
mxcl/swift-sh#113

[Jeehut]

@belkadan, @AnnaZaks, Jon (JIRA User): As nothing seems to happen here, I would be willing to fix this myself but I have no experience with contributing to a programming language, nor with compilers or with C++. I will try anyways, just to get things going and because this is marked as a starter bug. Let's see if it will turn out fine or not. Fingers crossed!

I've just created #31931 with what I understood from your text @belkadan, I hope I understood you correctly. Will try getting the environment running and updating the tests as suggested tomorrow (or once you confirmed I didn't misunderstand what you meant with "switching branches").