ABI checker: add a flag to opt-in diagnosing deprecated symbols

rdar://105255151

Author: nkcsgexi

include/swift/Option/Options.td

@@ -1541,6 +1541,10 @@ def disable_remove_deprecated_check: Flag<["-", "--"], "disable-remove-deprecate
   Flags<[NoDriverOption, SwiftAPIDigesterOption]>,
   HelpText<"Skip diagnosing removal of deprecated symbols">;
 
+def enable_remove_deprecated_check: Flag<["-", "--"], "enable-remove-deprecated-check">,
+  Flags<[NoDriverOption, SwiftAPIDigesterOption]>,
+  HelpText<"Diagnosing removal of deprecated symbols">;
+
 def print_module: Flag<["-", "--"], "print-module">,
   Flags<[NoDriverOption, SwiftAPIDigesterOption]>,
   HelpText<"Print module names in diagnostics">;

lib/DriverTool/swift_api_digester_main.cpp

@@ -2371,6 +2371,9 @@ class SwiftAPIDigesterInvocation {
         ParsedArgs.hasArg(OPT_abi) || ParsedArgs.hasArg(OPT_swift_only);
     CheckerOpts.SkipOSCheck = ParsedArgs.hasArg(OPT_disable_os_checks);
     CheckerOpts.SkipRemoveDeprecatedCheck = ParsedArgs.hasArg(OPT_disable_remove_deprecated_check);
+    if (ParsedArgs.hasArg(OPT_enable_remove_deprecated_check)) {
+      CheckerOpts.SkipRemoveDeprecatedCheck = false;
+    }
     CheckerOpts.CompilerStyle =
         CompilerStyleDiags || !SerializedDiagPath.empty();
     for (auto Arg : Args)