[mlir-opt] Don't enable `printOpOnDiagnostic` if it was explicitly disabled.

[rriddle]

Summary

We are currently explicitly setting the flag solely based on the value of -verify, which ends up ignoring the situation where the user explicitly disabled this option from the command line.

[mehdi_amini]

mlir/lib/Support/MlirOptMain.cpp

112–113

Isn't the context.shouldPrintOpOnDiagnostic() part redundant here?

[rriddle]

mlir/lib/Support/MlirOptMain.cpp

112–113

Yeah, it's cheap enough that it doesn't matter to check that here.

mlir/lib/Support/MlirOptMain.cpp

static LogicalResult processBuffer(raw_ostream &os,
   SourceMgr sourceMgr;
   sourceMgr.AddNewSourceBuffer(std::move(ownedBuffer), SMLoc());
 
   // Parse the input file.
   MLIRContext context(registry);
   if (preloadDialectsInContext)
     context.loadAllAvailableDialects();
   context.allowUnregisteredDialects(allowUnregisteredDialects);
-  context.printOpOnDiagnostic(!verifyDiagnostics);
+  if (verifyDiagnostics)
+    context.printOpOnDiagnostic(false);
   context.getDebugActionManager().registerActionHandler<DebugCounter>();
 
   // If we are in verify diagnostics mode then we have a lot of work to do,
   // otherwise just perform the actions without worrying about it.
   if (!verifyDiagnostics) {
     SourceMgrDiagnosticHandler sourceMgrHandler(sourceMgr, &context);
     return performActions(os, verifyDiagnostics, verifyPasses, sourceMgr,
                           &context, passPipeline);