Experimental support for CUDA

[varungandhi-src]

• (Trivial) Change the list of extensions for main TU files to also have "cu". feat: Add initial support for CUDA #433
• (Easy) Basic support for code nav for CUDAKernelCallExpr. feat: Initial code nav support for CUDA kernel call expressions #435
• (Unknown difficulty) Support for code nav for CUDAKernelCallExpr inside templates. Example: https://sourcegraph.com/github.com/apache/mxnet@b84609d/-/blob/src/operator/nn/pool.cuh?L111:17-111:39#tab=references (fix: Try to emit refs for unresolved call expressions #437)
• (Easy) Fix errors related to __clang_cuda_runtime_wrapper.h not being found (referenced from the <built-in> header for CUDA). feat: Auto-detect Clang directories when using NVCC #436
  • Uncertainty: Should we use -ccbin if present? It is absent when MXNet is compiled. And obviously GCC doesn't have this header.
• (Easy) Add the appropriate include directory for CUDA. It seems like the installation structure is

  $CUDA_DIR
    |-- bin
    |      \-- nvcc
    |-- include
  

  • Uncertainty: Will there be more include dirs needed once that one is fixed. feat: Add initial support for CUDA #433
• (Easy) Add documentation on using CUDA support/gotchas. docs: Mention CUDA gotchas and requirements in README #441
• (Easy-ish, a bit tedious) Zap unknown arguments (QOL improvement). fix: Remove a bunch of unknown NVCC-specific arguments #438

  error: unsupported option '--options-file=/home/varun/MDL-SDK/cmake/nvcc-option-use_fast_math.lst'
  error: unknown argument: '-forward-unknown-to-host-compiler'
  error: unknown argument: '-ccbin=/usr/bin/c++'
  error: unknown argument: '-rdc=true'
  error: unknown argument: '-forward-unknown-to-host-compiler'
  error: unknown argument '-arch=sm_50'; did you mean '-march=sm_50'?
  error: unknown argument: '-ptx'
  

  That said, maybe we should support --options-file by just inlining all the arguments from the file and then processing that?

[varungandhi-src]

Filed a separate issue for the GCC headers: #440