Fix hip _C_hip import for AMD supports internally (fairinternal/xform…

…ers#1057)

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__original_commit__ = fairinternal/xformers@bc9942a

xformers/_cpp_lib.py

@@ -115,7 +115,10 @@ def _register_extensions():
     )
 
     extfinder = importlib.machinery.FileFinder(lib_dir, loader_details)
-    ext_specs = extfinder.find_spec("_C")
+    if torch.version.hip and not hasattr(torch.version, "git_version"):
+        ext_specs = extfinder.find_spec("_C_hip")
+    else:
+        ext_specs = extfinder.find_spec("_C")
     if ext_specs is None:
         raise xFormersWasNotBuiltException()
     cpp_lib_json = os.path.join(lib_dir, "cpp_lib.json")