Merge pull request swiftlang#1586 from cachemeifyoucan/eng/PR-allow-cas-same-path

[Caching] Remove the error for creating multiple CAS at same location

Author: cachemeifyoucan

Sources/SwiftDriver/ExplicitModuleBuilds/InterModuleDependencies/InterModuleDependencyOracle.swift

@@ -189,12 +189,6 @@ public class InterModuleDependencyOracle {
  if let cas = createdCASMap[casOpt] {
  return cas
  }
- if let path = onDiskPath {
- guard !seenCASPath.contains(path) else {
- throw DependencyScanningError.casError("Cannot create two different CAS at the same OnDiskPath")
- }
- seenCASPath.insert(path)
- }
  let cas = try swiftScan.createCAS(pluginPath: pluginPath?.pathString, onDiskPath: onDiskPath?.pathString, pluginOptions: pluginOptions)
  createdCASMap[casOpt] = cas
  return cas
@@ -234,7 +228,5 @@ public class InterModuleDependencyOracle {
 
  /// Storing the CAS created via CASConfig.
  internal var createdCASMap: [CASConfig: SwiftScanCAS] = [:]
- /// The on disk path seen by CAS creation function.
- internal var seenCASPath: Set<AbsolutePath> = []
 }