[x265] cmake: avoid different stack alignment for GCC in 32-bit Windows

[Mateusz]

> I suggest use gcc option -mpreferred-stack-boundary
> 
> Min

If I change
add_definitions(-msse)
to
add_definitions(-mpreferred-stack-boundary=2)
it is working stable with all GCC that I tested (4.9.3, 5.4, 6.1, 7.0).
There is minimal slow-down with this change to GCC 5.4.

GCC 7.0 is working OK with current x265 code (so it is only GCC 6.1 problem).

MSVC is now default at SSE2 level for 32-bit target.
Intel Compiler is also at SSE2 level (-march=pentium4).
x264 ads for 32-bit GCC options: "-march=i686 -mfpmath=sse -msse -msse2" -- so it is also default at SSE2 level.

For me the best option is to change x265 default level for 32-bit GCC output to SSE2 (it was patch proposition 12954 from 2016-04-15, but it wasn't committed). It fixes GCC 6.1 problem and speed-up compression.

> At 2016-07-27 16:15:41,"Pradeep Ramachandran" <pradeep at multicorewareinc.com <mailto:pradeep at multicorewareinc.com>> wrote:
> 
>     `-msse` only enables the use of SSE instructions with GCC. Since we already add `-march=i686` which is Pentium Pro's instruction set, sse should anyways be added.
>     Why does adding this explicitly get rid of the stack misalignment problem that you are witnessing? Is there some new change to this option with 6.1 that I am missing?
> 
>     Pradeep.

'-march=i686' is without MMX nor SSE, so '-msse' changes a bit. GCC 6.1 is working OK with '-msse' option (but it is only workaround to GCC bug).

Mateusz

> 
>     On Tue, Jul 26, 2016 at 7:20 PM, Mateusz <mateuszb at poczta.onet.pl <mailto:mateuszb at poczta.onet.pl>> wrote:
> 
>         There are bugs in GCC 6.1 that prevent to compile working 32-bitx265for Windows(on default options).
>         This patch adds '-msse' option to default 32-bit build option to avoid different stack alignment.
> 
>         # HG changeset patch
>         # User Ma0 <mateuszb at poczta.onet.pl> <mailto:mateuszb at poczta.onet.pl>
>         # Date 1469540439 -7200
>         #      Tue Jul 26 15:40:39 2016 +0200
>         # Node ID b95ee119b5c6ccac4892c430c494d1a5f22b2ce0
>         # Parent  5a0e139e29386ecebafc9c555aedcd3e0f61c70c
>         cmake: avoid different stack alignment for GCC in 32-bit Windows
> 
>         diff -r 5a0e139e2938 -r b95ee119b5c6 source/CMakeLists.txt
>         --- a/source/CMakeLists.txt    Fri Jul 22 13:13:42 2016 +0530
>         +++ b/source/CMakeLists.txt    Tue Jul 26 15:40:39 2016 +0200
>         @@ -184,6 +184,9 @@
>                  string(FIND "${CMAKE_CXX_FLAGS}" "-march" marchPos)
>                  if(marchPos LESS "0")
>                      add_definitions(-march=i686)
>         +            if(WIN32 AND NOT INTEL_CXX)
>         +                add_definitions(-msse)
>         +            endif()
>                  endif()
>              endif()
>              if(ARM AND CROSS_COMPILE_ARM)
> 
> 
> 
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