Fix AVX2+ detection on Mac (#895)

MacOS is weird and its CPU flags are separated in two separate fields returned by the sysctl interface. To get around this, we need to test both of them, so here goes

Co-authored-by: Roman Grundkiewicz <rgrundkiewicz@gmail.com>

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Integrate a shortlist converter (which can convert a text lexical shortlist to a binary shortlist) into marian-conv with --shortlist option
 
 ### Fixed
+- Fix AVX2 and AVX512 detection on MacOS
 - Add GCC11 support into FBGEMM
 - Added pragma to ignore unused-private-field error on elementType_ on macOS
 - Do not set guided alignments for case augmented data if vocab is not factored

cmake/FindSSE.cmake

@@ -74,8 +74,7 @@ IF(CMAKE_SYSTEM_NAME MATCHES "Linux")
    ENDIF (AVX512_TRUE)
 
 ELSEIF(CMAKE_SYSTEM_NAME MATCHES "Darwin")
-   EXEC_PROGRAM("/usr/sbin/sysctl -n machdep.cpu.features" OUTPUT_VARIABLE
-      CPUINFO)
+   EXEC_PROGRAM("/usr/sbin/sysctl -n machdep.cpu.features machdep.cpu.leaf7_features" OUTPUT_VARIABLE CPUINFO)
 
    STRING(REGEX REPLACE "^.*[^S](SSE2).*$" "\\1" SSE_THERE ${CPUINFO})
    STRING(COMPARE EQUAL "SSE2" "${SSE_THERE}" SSE2_TRUE)