GH-126910: Make `_Py_get_machine_stack_pointer` return the stack poin… #2574

Job	Run time
aarch64-unknown-linux-gnu/gcc	8m 5s
aarch64-apple-darwin/clang	9m 49s
x86_64-unknown-linux-gnu/gcc-free-threading	8m 33s
x86_64-apple-darwin/clang	15m 55s
x86_64-unknown-linux-gnu/gcc	9m 30s
	51m 52s

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