The semantics associated with __vector [un]signed long are neither consistently specified nor consistently implemented. The IBM XL compilers on AIX traditionally treated these as deprecated aliases for the corresponding __vector int type in both 32-bit and 64-bit modes. The newer, Clang-based, IBM XL compilers on AIX make usage of the previously deprecated types an error. This is also consistent with IBM XL C/C++ for Linux on Power (on little endian distributions).
In line with the above, this patch upgrades (on AIX) the deprecation of __vector long to become removal.
minor nit, prefer to divide the comment in 2 sentences.