Fix AVX etc. under GCC/CMake (#1174)

CMakeLists.txt

@@ -270,16 +270,16 @@ else()
             set(CMAKE_C_FLAGS   "${CMAKE_C_FLAGS}   -pthread")
             set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
         else()
-            if(__AVX__)
+            if(NOT WHISPER_NO_AVX)
                 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mavx")
             endif()
-            if(__AVX2__)
+            if(NOT WHISPER_NO_AVX2)
                 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mavx2")
             endif()
-            if(__FMA__)
+            if(NOT WHISPER_NO_FMA)
                 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mfma")
             endif()
-            if(__F16C__)
+            if(NOT WHISPER_NO_F16C)
                 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mf16c")
             endif()
         endif()