MIR Parser: Use source locations for MBB naming errors.

This commit changes the type of the field 'Name' in the struct
'yaml::MachineBasicBlock' from 'std::string' to 'yaml::StringValue'. This change
allows the MIR parser to report errors related to the MBB name with the proper
source locations.

llvm-svn: 241718
diff --git a/llvm/lib/CodeGen/MIRPrinter.cpp b/llvm/lib/CodeGen/MIRPrinter.cpp
index 4a66365..a1f20f5 100644
--- a/llvm/lib/CodeGen/MIRPrinter.cpp
+++ b/llvm/lib/CodeGen/MIRPrinter.cpp
@@ -127,9 +127,9 @@
   YamlMBB.ID = (unsigned)MBB.getNumber();
   // TODO: Serialize unnamed BB references.
   if (const auto *BB = MBB.getBasicBlock())
-    YamlMBB.Name = BB->hasName() ? BB->getName() : "<unnamed bb>";
+    YamlMBB.Name.Value = BB->hasName() ? BB->getName() : "<unnamed bb>";
   else
-    YamlMBB.Name = "";
+    YamlMBB.Name.Value = "";
   YamlMBB.Alignment = MBB.getAlignment();
   YamlMBB.AddressTaken = MBB.hasAddressTaken();
   YamlMBB.IsLandingPad = MBB.isLandingPad();