PTX:  add PTX 2.3 language target

Patch by Wei-Ren Chen

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130980 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PTX/PTXSubtarget.cpp b/lib/Target/PTX/PTXSubtarget.cpp
index a224f2b..e754290 100644
--- a/lib/Target/PTX/PTXSubtarget.cpp
+++ b/lib/Target/PTX/PTXSubtarget.cpp
@@ -41,6 +41,7 @@
     case PTX_VERSION_2_0: return "2.0";
     case PTX_VERSION_2_1: return "2.1";
     case PTX_VERSION_2_2: return "2.2";
+    case PTX_VERSION_2_3: return "2.3";
   }
 }