CMake support on Linux for absence of AVX2.

CMakeLists.txt

@@ -166,7 +166,8 @@ else()
             if(NOT WHISPER_NO_AVX)
                 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mavx")
             endif()
-            if(NOT WHISPER_NO_AVX2)
+            execute_process(COMMAND cat /proc/cpuinfo COMMAND grep avx2 OUTPUT_VARIABLE FOUND_AVX2)
+            if(FOUND_AVX2 AND NOT WHISPER_NO_AVX2)
                 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mavx2")
             endif()
             if(NOT WHISPER_NO_FMA)