Attempt to fix AVX compilation issues on MacOS

The common wisdom is wrong, apparently: `-march=native` does not work
for AVX on MacOS.

Author: mhucka

pybind_interface/avx2/CMakeLists.txt

@@ -17,11 +17,7 @@ project(qsim)
 
 IF (WIN32)
     add_compile_options(/arch:AVX2)
-ELSEIF(APPLE AND NOT CMAKE_APPLE_SILICON_PROCESSOR)
-    # On Intel MacOS, CMake detects AVX* but clang doesn't recognize -mavx2.
-    # Using arch=native should turn on the features if they're available.
-    add_compile_options(-march=native)
-ELSE()
+ELSEIF(NOT CMAKE_APPLE_SILICON_PROCESSOR)
     add_compile_options(-mavx2 -mfma)
 ENDIF()
 

pybind_interface/avx512/CMakeLists.txt

@@ -17,11 +17,13 @@ project(qsim)
 
 IF (WIN32)
     add_compile_options(/arch:AVX512)
-ELSEIF(APPLE AND NOT CMAKE_APPLE_SILICON_PROCESSOR
+ELSEIF(APPLE
+       AND NOT CMAKE_APPLE_SILICON_PROCESSOR
        AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-    # On Intel Macs CMake detects AVX but clang doesn't recognize -mavx512.
-    # Using arch=native should turn on the features if they're available.
-    add_compile_options(-march=native)
+    # Note: some sources recommend against using -mavx512f, and say to use
+    # -march=native. The doesn't work on Mac Intel systems, at least in MacOS
+    # 13 (and possibly higher); the compiler does not enable AVX512 features.
+    add_compile_options(-mavx512f)
 ELSE()
     add_compile_options(-mavx512f -mbmi2)
 ENDIF()