Improve build comments and messaging

CMakeLists.txt

@@ -289,23 +289,26 @@ endmacro()
 # can be set to handle such cases.
 option(MY_ASSEMBLER_IS_TOO_OLD_FOR_AVX "Exclude AVX code from the build" OFF)
 
-# Some assemblers know about AVX but not AVX512 instructions, e.g. gcc 4.8.2.
+# Some assemblers know about AVX but not ADX, AVX2 or AVX512 instructions, e.g. gcc 4.8.2.
 # This flag can be set to handle such cases.
-# Note that the flag's name has "512AVX" instead of "AVX512" so that it doesn't
-# include the entire flag -DMY_ASSEMBLER_IS_TOO_OLD_FOR_AVX and match it
-# in the Perl files checks.
+# Note:
+# * Although this flag name implies an effect on AVX512 instructions, it's also
+#   intended to avoid generating ADX and AVX2 instructions.
+# * This flag name has "512AVX" instead of "AVX512" so that it doesn't
+#   include the entire flag -DMY_ASSEMBLER_IS_TOO_OLD_FOR_AVX and match
+#   to it in the Perl files checks.
 option(MY_ASSEMBLER_IS_TOO_OLD_FOR_512AVX "Exclude AVX512 code from the build" OFF)
 
 if(MY_ASSEMBLER_IS_TOO_OLD_FOR_AVX)
   add_definitions(-DMY_ASSEMBLER_IS_TOO_OLD_FOR_AVX)
   add_definitions(-DMY_ASSEMBLER_IS_TOO_OLD_FOR_512AVX)
   set(MY_ASSEMBLER_IS_TOO_OLD_FOR_512AVX ON)
-  message(STATUS "MY_ASSEMBLER_IS_TOO_OLD_FOR_AVX selected, removing AVX optimisations")
+  message(STATUS "MY_ASSEMBLER_IS_TOO_OLD_FOR_AVX selected, removing all AVX optimisations")
 endif()
 
 if(MY_ASSEMBLER_IS_TOO_OLD_FOR_512AVX)
   add_definitions(-DMY_ASSEMBLER_IS_TOO_OLD_FOR_512AVX)
-  message(STATUS "MY_ASSEMBLER_IS_TOO_OLD_FOR_512AVX selected, removing AVX512 optimisations")
+  message(STATUS "MY_ASSEMBLER_IS_TOO_OLD_FOR_512AVX selected, removing ADX, AVX2 and AVX512 optimisations")
 endif()
 
 if (GCC)