simplify file comparison

[Cherry-picked 246dfc4][modified]

Author: Kordyjan

compiler/src/dotty/tools/dotc/sbt/ExtractDependencies.scala

@@ -138,15 +138,12 @@ class ExtractDependencies extends Phase {
 
     val depFile = dep.to.associatedFile
     if (depFile != null) {
-      def depIsSameSource =
-        depFile.absolutePath == sourceFile.file.absolutePath
-
       // Cannot ignore inheritance relationship coming from the same source (see sbt/zinc#417)
       def allowLocal = dep.context == DependencyByInheritance || dep.context == LocalDependencyByInheritance
       if (depFile.extension == "class") {
         // Dependency is external -- source is undefined
         processExternalDependency(depFile, dep.to.binaryClassName)
-      else if (allowLocal || !depIsSameSource /* old: depFile.file != sourceFile.file */) {
+      } else if (allowLocal || depFile != sourceFile.file) {
         // We cannot ignore dependencies coming from the same source file because
         // the dependency info needs to propagate. See source-dependencies/trait-trait-211.
         val toClassName = classNameAsString(dep.to)