Change the error message when -split-input-file is used with mlir-opt to make it recognizable by IDEs

By adding the line number of the split point immediately after the file
name (separated by `:`) this is recognized by various tool as a proper
location.

Ideally we would want to point to the line of the error, but that would
require some very invasive changes I suspect.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D93363

mlir/lib/Support/ToolUtilities.cpp

@@ -37,8 +37,9 @@ mlir::splitAndProcessBuffer(std::unique_ptr<llvm::MemoryBuffer> originalBuffer,
     auto splitLoc = llvm::SMLoc::getFromPointer(subBuffer.data());
     unsigned splitLine = fileSourceMgr.getLineAndColumn(splitLoc).first;
     auto subMemBuffer = llvm::MemoryBuffer::getMemBufferCopy(
-        subBuffer, origMemBuffer->getBufferIdentifier() +
-                       Twine(" split at line #") + Twine(splitLine));
+        subBuffer, Twine("within split at ") +
+                       origMemBuffer->getBufferIdentifier() + ":" +
+                       Twine(splitLine) + " offset ");
     if (failed(processChunkBuffer(std::move(subMemBuffer), os)))
       hadFailure = true;
   }