Add various target-specific and compiler-determined paths to the output
of `-print-target-info`, such as the runtime resource path, SDK path, and
runtime library paths.
Rather than only emitting the target triple, provide additional
information about that particular target, including the module triple
(i.e., what file names will be used for Swift modules for that
triple), the runtime compatibility version if there is one, and
whether linking with rpaths is required for the standard library and
other libraries shipped with Swift. Encode this as JSON so we can
extend it in the future. For now, it looks like this:
```
{
"target": {
"triple": "arm64-apple-ios12.0",
"moduleTriple": "arm64-apple-ios",
"swiftRuntimeCompatibilityVersion": "5.0",
"librariesRequireRPath": true
}
}
```
Which you can deserialize into a TargetInfo instance as defined below:
```
struct Target: Codable {
/// The target triple.
var triple: String
/// The triple used for module file names.
var moduleTriple: String
/// If this platform provides the Swift runtime, the Swift language
version
/// with which that runtime is compatible.
var swiftRuntimeCompatibilityVersion: String?
/// Whether linking against the Swift libraries requires the use of
rpaths.
var librariesRequireRPath: Bool
}
struct TargetInfo: Codable {
var target: Target
}
```
Implements rdar://problem/47095159.
