Enable new #file in Swift 6 mode

This change was approved for Swift 6 mode in SE-0274/SE-0285.

Author: beccadax

lib/Frontend/CompilerInvocation.cpp

@@ -654,7 +654,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   }
 
   Opts.EnableConcisePoundFile =
-      Args.hasArg(OPT_enable_experimental_concise_pound_file);
+      Args.hasArg(OPT_enable_experimental_concise_pound_file) ||
+      Opts.EffectiveLanguageVersion.isVersionAtLeast(6);
   Opts.EnableFuzzyForwardScanTrailingClosureMatching =
       Args.hasFlag(OPT_enable_fuzzy_forward_scan_trailing_closure_matching,
                    OPT_disable_fuzzy_forward_scan_trailing_closure_matching,

test/Sema/diag_mismatched_magic_literals_swift6.swift

@@ -1,6 +1,10 @@
 // The future "Swift 6 mode" behavior is staged in behind  `-enable-experimental-concise-pound-file`.
 // RUN: %target-typecheck-verify-swift -enable-experimental-concise-pound-file
 
+// And is also available in Swift 6 mode on asserts compilers.
+// RUN: %target-typecheck-verify-swift -swift-version 6
+// REQUIRES: asserts
+
 func callee(file: String = #file) {} // expected-note {{'file' declared here}}
 func callee(fileID: String = #fileID) {} // expected-note {{'fileID' declared here}}
 func callee(filePath: String = #filePath) {} // expected-note 2 {{'filePath' declared here}}