ext: clang fix for flexible array members
ext: clang fix for flexible array members

Changes how flexible array members are defined so clang does not error
out during compilation.
(transplanted from 0edd36ea6130cefd976393e02f624e7124a06de4)

LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5