[IC] IC should allow source files without common root with the buildDir

^KT-63983 Fixed
diff --git a/build-common/src/org/jetbrains/kotlin/incremental/storage/RelocatableFileToPathConverter.kt b/build-common/src/org/jetbrains/kotlin/incremental/storage/RelocatableFileToPathConverter.kt
index 8a66cec..31648fd 100644
--- a/build-common/src/org/jetbrains/kotlin/incremental/storage/RelocatableFileToPathConverter.kt
+++ b/build-common/src/org/jetbrains/kotlin/incremental/storage/RelocatableFileToPathConverter.kt
@@ -21,7 +21,7 @@
 
         // Note: If the given file is located outside `baseDir`, the relative path will start with "../". It's not "clean", but it can work.
         // TODO: Re-design the code such that `baseDir` always contains the given file (also add a precondition check here).
-        return file.relativeTo(baseDir).invariantSeparatorsPath
+        return file.relativeToOrSelf(baseDir).invariantSeparatorsPath
     }
 
     override fun toFile(path: String): File {