[ABIChecker] Use -Isystem and -Fsystem for swift-api-digester

[ian-twilightcoder]

Use the Swift -Fsystem flag for swift-api-digester instead of the clang -iframework flag. Add support for -Isystem for parity.

rdar://152747420

[cachemeifyoucan]

Code change LGTM. You probably want to get the swift driver change in before compiler dropping the flag, or support both flags for a while but change swift-driver to prefer -Isystem and -Fsystem.

[ian-twilightcoder]

Code change LGTM. You probably want to get the swift driver change in before compiler dropping the flag, or support both flags for a while but change swift-driver to prefer -Isystem and -Fsystem.

Is it good enough to land the swift-driver change at the same time, or should we support both for a little while?

[cachemeifyoucan]

Is it good enough to land the swift-driver change at the same time, or should we support both for a little while?

We need to support mismatched version for a while. SwiftDriver can be ahead or behind. The compatibility can be done in compiler or driver or both, just need to support mismatch. I don't know when APIDigester is used so maybe we can have a even smaller range of mismatched version.

[ian-twilightcoder]

Is it good enough to land the swift-driver change at the same time, or should we support both for a little while?

We need to support mismatched version for a while. SwiftDriver can be ahead or behind. The compatibility can be done in compiler or driver or both, just need to support mismatch. I don't know when APIDigester is used so maybe we can have a even smaller range of mismatched version.

Alright, putting -iframework back.

[cachemeifyoucan]

Other than one file change. Otherwise LGTM.

[ian-twilightcoder]

@swift-ci smoke test