Requiring SSE2 on Windows

 Hello,

 I suggest that we remove the '-arch:SSE' added on Windows, i.e. that we 
require at least SSE2-capable systems.

 This was added by 8bd6bf93b7 in 2014, but at this point there's basically 
nobody who would be running LO but wouldn't be capable of SSE2.

 Some relevant facts:
- GCC, Clang and MSVC all default to SSE2+
- The last Windows to work without at least SSE2 was Windows 7, which is EOL 
(and in fact it in practice required SSE2+ too, since an update in 2018).
- Windows 8, MSOffice 2013, Chromium require SSE2+.
- I checked all ~240k crash dumps reported in the last month and there's not a 
single one from a machine not capable of SSE2.

-- 
 Luboš Luňák
 l.lunak@collabora.com