Bug#1033656: HWY_CMAKE_ARM7:BOOL=ON vs Dynamic Dispatch

[Mathieu Malaterre]

Control: forwarded -1 https://github.com/google/highway/issues/1271

Technically we could just do a source upload with
HWY_CMAKE_ARM7:BOOL=OFF. HWY_CMAKE_ARM7:BOOL=ON is a hack for an old
clang version, if I understand correctly.