[3.14] gh-135755: rename undocumented `HACL_CAN_COMPILE_SIMD{128,256}` macros (GH-135847) (#136045)

Rename undocumented `HACL_CAN_COMPILE_SIMD{128,256}` macros
to `_Py_HACL_CAN_COMPILE_VEC{128,256}`. These macros are private.
(cherry picked from commit 1e975aee28924afbd956183918cef278e09ce8f3)