[readtapi] add optional --<option>"=" to some cli opts (llvm#72426)

(cherry picked from commit 3b48a7a)

Author: cyndyishida

llvm/tools/llvm-readtapi/TapiOpts.td

@@ -2,13 +2,16 @@
 include "llvm/Option/OptParser.td"
 
 class FF<string name, string help>: Flag<["-", "--"], name>, HelpText<help>;
-class JS<string name, string help, string var = ""> : JoinedOrSeparate<["-", "--"], name>, HelpText<help>, MetaVarName<var>;
+multiclass JS<string name, string help, string var = ""> {
+  def NAME #_EQ : Joined<["--"], name #"=">, HelpText<help>, MetaVarName<var>;
+  def : Separate<["-", "--"], name>, Alias<!cast<Joined>(NAME #_EQ)>;
+}
 
 //
 // General Driver options 
 //
 def help : FF<"help", "display this help">;
-def output: JS<"o", "write output to <file>","<file>">;
+defm output: JS<"o", "write output to <file>","<file>">;
 
 //
 // Compare options

llvm/tools/llvm-readtapi/llvm-readtapi.cpp

@@ -127,7 +127,7 @@ int main(int Argc, char **Argv) {
   for (opt::Arg *A : Args.filtered(OPT_INPUT))
     Ctx.Inputs.push_back(A->getValue());
 
-  if (opt::Arg *A = Args.getLastArg(OPT_output)) {
+  if (opt::Arg *A = Args.getLastArg(OPT_output_EQ)) {
     std::string OutputLoc = std::move(A->getValue());
     std::error_code EC;
     Ctx.OutStream = std::make_unique<llvm::raw_fd_stream>(OutputLoc, EC);