aes-ni.c pushes its target attribute under #ifdef __clang__ but pops it
under #ifdef _WIN64. For clang targeting Win64 the two coincide. Otherwise
they do not: clang targeting 32-bit Windows (clang-cl in a WINSCP_VS build)
reports the push as unterminated and fails, and MSVC targeting x64 meets a
pop of a clang pragma it does not know (warning C4068). The pop now has the
push's condition.
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