[RUNTIME] remove fixed cu_include_dir (#739)

Use environment variable `CUDA_HOME` with default value`/usr/local/cuda` for `cu_include_dir` #731

python/triton/compiler.py

@@ -1107,6 +1107,12 @@ def libcuda_dirs():
     return [os.path.dirname(loc) for loc in locs]
 
 
+@functools.lru_cache()
+def cuda_home_dirs():
+    default_dir = "/usr/local/cuda"
+    return os.getenv("CUDA_HOME", default=default_dir)
+
+
 @contextlib.contextmanager
 def quiet():
     old_stdout, old_stderr = sys.stdout, sys.stderr
@@ -1119,7 +1125,7 @@ def quiet():
 
 def _build(name, src, srcdir):
     cuda_lib_dirs = libcuda_dirs()
-    cu_include_dir = "/usr/local/cuda/include"
+    cu_include_dir = os.path.join(cuda_home_dirs(), "include")
     suffix = sysconfig.get_config_var('EXT_SUFFIX')
     so = os.path.join(srcdir, '{name}{suffix}'.format(name=name, suffix=suffix))
     # try to avoid setuptools if possible