[test] diff --strip-trailing-cr is non-standard.

This flag is a GNU extension, and would cause misleading test failures
on other platforms where this extension is not available. However, the
necessity to switch line endings is only required on Windows when
testing. We could use sed to canonicalize line endings before comparing,
but that may cause higher amounts of filesystem traffic on Windows which
would slow down testing.

Instead, move the substitution for diff in SourceKit's lit.local.cfg up
to the top level, and conditionalize the substitution which has the flag
on Windows, but not on other platforms (where it should not be required).

Author: 3405691582

test/Migrator/double_fixit_ok.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: not %target-swift-frontend -typecheck -update-code -primary-file %s -emit-migrated-file-path %t/double_fixit_ok.result -swift-version 4
-// RUN: diff --strip-trailing-cr -u %s.expected %t/double_fixit_ok.result
+// RUN: %diff -u %s.expected %t/double_fixit_ok.result
 // RUN: %target-swift-frontend -typecheck %s.expected -swift-version 5
 
 @available(swift, obsoleted: 4, renamed: "Thing.constant___renamed")

test/Migrator/double_fixit_ok.swift.expected

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: not %target-swift-frontend -typecheck -update-code -primary-file %s -emit-migrated-file-path %t/double_fixit_ok.result -swift-version 4
-// RUN: diff --strip-trailing-cr -u %s.expected %t/double_fixit_ok.result
+// RUN: %diff -u %s.expected %t/double_fixit_ok.result
 // RUN: %target-swift-frontend -typecheck %s.expected -swift-version 5
 
 @available(swift, obsoleted: 4, renamed: "Thing.constant___renamed")

test/Migrator/insert_replace_fixit.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -typecheck -update-code -primary-file %s -F %S/mock-sdk -emit-migrated-file-path %t/result.swift -swift-version 4
-// RUN: diff --strip-trailing-cr -u %s.expected %t/result.swift
+// RUN: %diff -u %s.expected %t/result.swift
 
 import TestMyTime
 

test/Migrator/insert_replace_fixit.swift.expected

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -typecheck -update-code -primary-file %s -F %S/mock-sdk -emit-migrated-file-path %t/result.swift -swift-version 4
-// RUN: diff --strip-trailing-cr -u %s.expected %t/result.swift
+// RUN: %diff -u %s.expected %t/result.swift
 
 import TestMyTime
 

test/Migrator/no_extraneous_argument_labels.swift

@@ -1,6 +1,6 @@
 // RUN: %target-swift-frontend -typecheck %s -swift-version 4
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -primary-file %s -emit-migrated-file-path %t/no_extraneous_argument_labels.result -swift-version 4 -o /dev/null
-// RUN: diff --strip-trailing-cr -u %s.expected %t/no_extraneous_argument_labels.result
+// RUN: %diff -u %s.expected %t/no_extraneous_argument_labels.result
 // RUN: %target-swift-frontend -typecheck %s.expected -swift-version 5
 
 func foo(_ oc: [String]) {

test/Migrator/no_extraneous_argument_labels.swift.expected

@@ -1,6 +1,6 @@
 // RUN: %target-swift-frontend -typecheck %s -swift-version 4
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -primary-file %s -emit-migrated-file-path %t/no_extraneous_argument_labels.result -swift-version 4 -o /dev/null
-// RUN: diff --strip-trailing-cr -u %s.expected %t/no_extraneous_argument_labels.result
+// RUN: %diff -u %s.expected %t/no_extraneous_argument_labels.result
 // RUN: %target-swift-frontend -typecheck %s.expected -swift-version 5
 
 func foo(_ oc: [String]) {

test/Migrator/no_var_to_let.swift

@@ -1,7 +1,7 @@
 // RUN: %target-swift-frontend -typecheck %s -swift-version 4
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -emit-migrated-file-path %t/no_var_to_let.swift.result -swift-version 4 -o /dev/null
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -emit-migrated-file-path %t/no_var_to_let.swift.result -swift-version 4 -o /dev/null
-// RUN: diff --strip-trailing-cr -u %s %t/no_var_to_let.swift.result
+// RUN: %diff -u %s %t/no_var_to_let.swift.result
 // RUN: %target-swift-frontend -typecheck %s -swift-version 5
 
 // Note that the diff run line indicates that there should be no change.

test/Migrator/null_migration.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t) && %target-swift-frontend -c -update-code -primary-file %s -emit-migrated-file-path %t/migrated_null_migration.swift -emit-remap-file-path %t/null_migration.remap -o /dev/null
-// RUN: diff --strip-trailing-cr -u %s %t/migrated_null_migration.swift
+// RUN: %diff -u %s %t/migrated_null_migration.swift
 
 // This file tests that, if all migration passes are no-op,
 // there are no changes to the file.

test/Migrator/optional_try_migration.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -c -swift-version 4 -primary-file %s -emit-migrated-file-path %t/optional_try_migration.result.swift
-// RUN: diff --strip-trailing-cr -u %S/optional_try_migration.swift.expected %t/optional_try_migration.result.swift
+// RUN: %diff -u %S/optional_try_migration.swift.expected %t/optional_try_migration.result.swift
 
 func fetchOptInt() throws -> Int? {
     return 3

test/Migrator/optional_try_migration.swift.expected

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -c -swift-version 4 -primary-file %s -emit-migrated-file-path %t/optional_try_migration.result.swift
-// RUN: diff --strip-trailing-cr -u %S/optional_try_migration.swift.expected %t/optional_try_migration.result.swift
+// RUN: %diff -u %S/optional_try_migration.swift.expected %t/optional_try_migration.result.swift
 
 func fetchOptInt() throws -> Int? {
     return 3