[CUDA] Add Target::isNVPTX().

[jlebar]

Summary

Helper so we don't have to enumerate nvptx && nvptx64 everywhere.

[echristo]

OK.

include/llvm/ADT/Triple.h

public:
   bool isPS4() const {
     return getVendor() == Triple::SCEI &&
            getOS() == Triple::PS4;
   }
 
   /// Tests whether the target is Android
   bool isAndroid() const { return getEnvironment() == Triple::Android; }
 
+  /// Tests whether the target is NVPTX (32- or 64-bit).
+  bool isNVPTX() const {
+    return getArch() == Triple::nvptx || getArch() == Triple::nvptx64;
+  }
+
   /// @}
   /// @name Mutators
   /// @{
 
   /// setArch - Set the architecture (first) component of the triple
   /// to a known type.
   void setArch(ArchType Kind);