Add warning for Turing GPUs and CUDA <= 9000 (pytorch#21468)

Summary:
Turing GPUs (compute capability 7.5) require CUDA10 to work properly.
We've seen some issues for these GPUs using PyTorch binaries with CUDA9 or older:
[Discussion Board pytorch#1](https://discuss.pytorch.org/t/cudnn-status-execution-failed-error/38575)
[Discussion Board pytorch#2](https://discuss.pytorch.org/t/cublas-runtime-error-on-gpu-running-but-works-on-cpu/46545/6)

Tested on using CUDA9 with an RTX 2080Ti.
Pull Request resolved: pytorch#21468

Differential Revision: D15696170

Pulled By: ezyang

fbshipit-source-id: ed43f4e4948d3f97ec8e7d7952110cbbfeafef2a

torch/cuda/__init__.py

@@ -110,8 +110,8 @@ def _check_driver():
 
 def _check_capability():
     incorrect_binary_warn = """
-    Found GPU%d %s which requires CUDA_VERSION >= %d for
-     optimal performance and fast startup time, but your PyTorch was compiled
+    Found GPU%d %s which requires CUDA_VERSION >= %d to
+     work properly, but your PyTorch was compiled
      with CUDA_VERSION %d. Please install the correct PyTorch binary
      using instructions from https://pytorch.org
     """
@@ -126,9 +126,12 @@ def _check_capability():
     for d in range(device_count()):
         capability = get_device_capability(d)
         major = capability[0]
+        minor = capability[1]
         name = get_device_name(d)
         if capability == (3, 0) or major < 3:
             warnings.warn(old_gpu_warn % (d, name, major, capability[1]))
+        elif CUDA_VERSION <= 9000 and major >= 7 and minor >= 5:
+            warnings.warn(incorrect_binary_warn % (d, name, 10000, CUDA_VERSION))
 
 
 def _lazy_call(callable):