Add support for Apple M1 AArch64 SoCs (#204)

* Add support for Apple M1 AArch64 SoCs

Completely based on #150. Thanks to @sbehnke!
+ Refactoring to accomodate the new source tree
+ Adding more feature flags

* revert minimum version to 3.0

* Update introspection table

* Simplify logic for Apple HAVE_SYSCTLBYNAME

---------

Co-authored-by: Guillaume Chatelet <gchatelet@google.com>

README.md

@@ -182,7 +182,7 @@ flags           : aes,avx,cx16,smx,sse4_1,sse4_2,ssse3
 |---------|:----:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|
 | Linux   | yes² | yes¹    | yes¹    | yes¹    | yes¹    | yes¹    | yes¹    |
 | FreeBSD | yes² | not yet | not yet | not yet | not yet | N/A     | not yet |
-| MacOs   | yes² | not yet | N/A     | N/A     | no      | N/A     | no      |
+| MacOs   | yes² | yes⁵    | N/A     | N/A     | N/A     | N/A     | N/A     |
 | Windows | yes² | not yet | not yet | N/A     | N/A     | N/A     | N/A     |
 | Android | yes² | yes¹    | yes¹    | yes¹    | N/A     | N/A     | N/A     |
 | iOS     | N/A  | not yet | not yet | N/A     | N/A     | N/A     | N/A     |
@@ -200,6 +200,8 @@ flags           : aes,avx,cx16,smx,sse4_1,sse4_2,ssse3
     microarchitecture allows the client to reject particular microarchitectures.
 4.  All flavors of Mips are supported, little and big endian as well as 32/64
     bits.
+5.  **Features revealed from sysctl.** features are retrieved by the `sysctl`
+    instruction.
 
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 ## Android NDK's drop in replacement