Fix importlib issues (#80)

The previous implementation worked on Python 3.11 but had a host of issues with
other versions. It boiled down to `triton._C` not being a regular package -- it
doesn't have an `__init__.py` file. However, it can still be imported as a
[namespace package][1]. Namespace packages can map to multiple locations on the
filesystem, so we cannot get a path to the package contents without
materializing the package.

The solution is to look up the files of the top-level `triton` package instead,
which is a regular package, and use that to find the location of the `_C`
directory.

I've tested that this approach works on 3.9 and 3.12 in macOS.

Fixes #76.

[1]: https://packaging.python.org/en/latest/guides/packaging-namespace-packages/#native-namespace-packages

third_party/cpu/backend/driver.py

@@ -12,7 +12,7 @@
 
 _dirname = os.getenv("TRITON_SYS_PATH", default="/usr/local")
 # for locating libTritonCPURuntime
-_triton_C_dir = importlib.resources.files(triton._C).joinpath("")
+_triton_C_dir = importlib.resources.files(triton).joinpath("_C")
 
 include_dirs = [os.path.join(_dirname, "include")]
 library_dirs = [os.path.join(_dirname, "lib"), _triton_C_dir]