[FRONTEND] change hash to not require ptxas (#2476)

I noticed that Triton is using the `ptxas` version as part of the
version hash even for non-CUDA targets. This is an attempt at fixing
this. Moving the version calculation to the back-end makes sense to me
from an architectural standpoint, so that's my approach here. I'm not as
confident in the implementation, so please if folks have any feedback
let me know.

python/test/backend/test_device_backend.py

@@ -13,12 +13,12 @@ import torch
 
 import triton
 import triton.language as tl
-from triton.common.backend import BaseBackend, register_backend
+from triton.common.backend import (BaseBackend, compute_core_version_key,
+                                   register_backend)
 from triton.common.build import quiet
 from triton.compiler.make_launcher import make_so_cache_key
 from triton.runtime.cache import get_cache_manager
 from triton.runtime.driver import DriverBase
-from triton.runtime.jit import version_key
 
 
 def build_for_backend(name, src, srcdir):
@@ -125,6 +125,7 @@ class ExtensionBackend(BaseBackend):
     def __init__(self, device_type: str) -> None:
         super(ExtensionBackend, self).__init__(device_type)
         self.driver = ExtensionDriver()
+        self.version_key = None
 
     def add_stages(self, arch, extern_libs, stages):
         filter_in_stages = ["ast", "ttir", "ttgir"]
@@ -163,9 +164,14 @@ class ExtensionBackend(BaseBackend):
     def get_architecture_descriptor(self, **kwargs):
         return ""
 
+    def get_version_key(self):
+        if self.version_key is None:
+            self.version_key = compute_core_version_key()
+        return self.version_key
+
     def make_launcher_stub(self, name, signature, constants):
         # name of files that are cached
-        so_cache_key = make_so_cache_key(version_key(), signature, constants)
+        so_cache_key = make_so_cache_key(self.get_version_key(), signature, constants)
         so_cache_manager = get_cache_manager(so_cache_key)
         so_name = f"{name}.so"
         # retrieve stub from cache if it exists