Fix radeonsi rusticl regression when pack_32_4x8_split
AMD compiler backend does not implement it, so don't lower pack_32_4x8 to pack_32_4x8_split.
For #11781 (closed)
Edited by Qiang Yu
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AMD compiler backend does not implement it, so don't lower pack_32_4x8 to pack_32_4x8_split.
For #11781 (closed)