* Simple boilerplate for GPU runtime files

  - GPUBackend
  - GPU ExternalFunction
  - GPUManager
  - GPUCallFrame

* Test for construction all GPU runtime classes

* Comment out calls, constructors haven't been defined

* Clang CUDA source example to later test compiling

Clang cuda example from:
https://gist.github.com/anonymous/855e277884eb6b388cd2f00d956c2fd4

* Initial nvptx compiler copied from CPU compiler sources

* Define FunctionMap and Instruction for gpu external function

* Rename Compiler -> NVPTXCompiler for gpu compile. Add call to compile for test

* Rename StaticCompiler -> NVPTXStaticCompiler for GPU code gen

* CAdd nvptx_compiler and nvptx_execution_engine to gpu sources

* Compiling source unit test using hardcoded PTX

* (a+b)*c test for GPU

* WIP Fix compile

* rmed accidentally included file

* Fix compile, and LLVM link errosr from nvptx_compiler.cpp

* Stub out parts needed for GPU manager

* Test GPU runtime method stubs

* Cleanup

* Add GPU runtime to same cmake block as GPU, include CUDA headers if GPU enabled

* Kill reflexive assertion

* change GPU naming convention to match CPU

* Snake case functions and identifiers in test case

* Change element type to match changes in master

* Make CUDA headers accessible for codegen with GPU transformer

* clang-format

* apply-code-format