llvm-undname: Support demangling char8_t

Ports clang's mangling support added in r354633 to llvm-undname.

llvm-svn: 361839
diff --git a/llvm/lib/Demangle/MicrosoftDemangle.cpp b/llvm/lib/Demangle/MicrosoftDemangle.cpp
index 4abb48e..425c7d3 100644
--- a/llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ b/llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -1944,6 +1944,8 @@
       return Arena.alloc<PrimitiveTypeNode>(PrimitiveKind::Uint64);
     case 'W':
       return Arena.alloc<PrimitiveTypeNode>(PrimitiveKind::Wchar);
+    case 'Q':
+      return Arena.alloc<PrimitiveTypeNode>(PrimitiveKind::Char8);
     case 'S':
       return Arena.alloc<PrimitiveTypeNode>(PrimitiveKind::Char16);
     case 'U':