[mlir][llvm] Keep unhandled constant test.

[gysit]

Summary

Add the more precise error message introduced in
https://reviews.llvm.org/D142337 to the standard
error produced for unhandled constants. This way
we keep testing both error cases.

[Dinistro]

LGTM!

mlir/lib/Target/LLVMIR/ModuleImport.cpp

for (const auto &it : llvm::enumerate(elementValues)) {
             builder.create<ConstantOp>(loc, builder.getI32Type(), indexAttr);
         root = builder.create<InsertElementOp>(loc, rootType, root, it.value(),
                                                indexValue);
       }
     }
     return root;
   }
 
-  if (isa<llvm::BlockAddress>(constant)) {
-    return emitError(loc)
-           << "blockaddress is not implemented in the LLVM dialect";
-  }
+  StringRef error = "";
+  if (isa<llvm::BlockAddress>(constant))
+    error = " since blockaddress(...) is unsupported";
 
-  return emitError(loc) << "unhandled constant: " << diag(*constant);
+  return emitError(loc) << "unhandled constant: " << diag(*constant) << error;
 }
 
 FailureOr<Value> ModuleImport::convertConstantExpr(llvm::Constant *constant) {
   assert(constantInsertionBlock &&
          "expected the constant insertion block to be non-null");
 
   // Insert the constant after the last one or at the start or the entry block.
   OpBuilder::InsertionGuard guard(builder);

mlir/test/Target/LLVMIR/Import/import-failure.ll

 define i32 @unhandled_value(i32 %arg1) {
   %1 = call i32 asm "bswap $0", "=r,r"(i32 %arg1)
   ret i32 %1
 }
 
 ; // -----
 
 ; CHECK:      import-failure.ll
-; CHECK-SAME: error: blockaddress is not implemented in the LLVM dialect
+; CHECK-SAME: unhandled constant: ptr blockaddress(@unhandled_constant, %bb1) since blockaddress(...) is unsupported
 ; CHECK:      import-failure.ll
 ; CHECK-SAME: error: unhandled instruction: ret ptr blockaddress(@unhandled_constant, %bb1)
 define ptr @unhandled_constant() {
   br label %bb1
 bb1:
   ret ptr blockaddress(@unhandled_constant, %bb1)
 }
 
 ; // -----
 
 ; CHECK:      import-failure.ll
-; CHECK-SAME: error: blockaddress is not implemented in the LLVM dialect
+; CHECK-SAME: unhandled constant: ptr blockaddress(@unhandled_global, %bb1) since blockaddress(...) is unsupported
 ; CHECK:      import-failure.ll
 ; CHECK-SAME: error: unhandled global variable: @private = private global ptr blockaddress(@unhandled_global, %bb1)
 @private = private global ptr blockaddress(@unhandled_global, %bb1)
 
 define void @unhandled_global() {
   br label %bb1
 bb1:
   ret void