[MLIR] Flag no-terminator error on the last operation of non-empty blocks

- When a block is not empty and does not end with a terminator, flag the error on the
  last operation of the block instead of the start of the block.

Differential Revision: https://reviews.llvm.org/D90988

mlir/lib/IR/Verifier.cpp

@@ -148,7 +148,7 @@ LogicalResult OperationVerifier::verifyBlock(Block &block) {
   if (failed(verifyOperation(block.back())))
     return failure();
   if (block.back().isKnownNonTerminator())
-    return emitError(block, "block with no terminator");
+    return block.back().emitError("block with no terminator");
 
   // Verify that this block is not branching to a block of a different
   // region.

mlir/test/IR/invalid.mlir

@@ -170,7 +170,8 @@ func @block_first_has_predecessor() {
 // -----
 
 func @no_return() {
-  %x = constant 0 : i32  // expected-error {{block with no terminator}}
+  %x = constant 0 : i32
+  %y = constant 1 : i32  // expected-error {{block with no terminator}}
 }
 
 // -----