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/test/CodeGen/MIR/machine-basic-block-unknown-name.mir b/llvm/test/CodeGen/MIR/machine-basic-block-unknown-name.mir
index ed675c5e..df8eee9 100644
--- a/llvm/test/CodeGen/MIR/machine-basic-block-unknown-name.mir
+++ b/llvm/test/CodeGen/MIR/machine-basic-block-unknown-name.mir
@@ -13,7 +13,7 @@
 ---
 name:            foo
 body:
-  # CHECK: basic block 'entrie' is not defined in the function 'foo'
+  # CHECK: [[@LINE+2]]:18: basic block 'entrie' is not defined in the function 'foo'
   - id:          0
     name:        entrie
 ...