add native aarch64 (arm64) support

use -mcpu=native on arm64 targets

build-appimage.sh kernel architecture detection

runtime/cmake/PublicProducts.cmake

@@ -298,11 +298,26 @@ else()
     message(STATUS "RetroRewind target disabled (run translate-mod and emit-build-shards)")
 endif()
 
+# x86-64-v3 (SSE3/SSSE3/SSE4.1/FMA/AVX2/BMI2) is the baseline runtime/src/host_cpu_baseline.cpp
+# guards against - a fixed, portable floor since an x86_64 build may run on a different machine
+# than the one that built it. AArch64 has no such redistribution path here: every build this
+# project produces runs only on the machine that built it (local-build.sh, and the AppImage which
+# wraps it, always build from source on the target), so -mcpu=native is safe and strictly better -
+# real per-core tuning (scheduling, whatever NEON/atomic extensions that exact CPU actually has)
+# instead of the generic armv8-a baseline Clang would otherwise assume.
+if(CMAKE_SYSTEM_PROCESSOR MATCHES "^(AMD64|amd64|x86_64|X86_64)$")
+    set(MKW_BASELINE_ARCH_FLAG -march=x86-64-v3)
+elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "^(aarch64|arm64|ARM64)$")
+    set(MKW_BASELINE_ARCH_FLAG -mcpu=native)
+else()
+    set(MKW_BASELINE_ARCH_FLAG "")
+endif()
+
 set(MKW_ALL_BUILD_TARGETS
     mkw_runtime_common mkw_base_shared mkw_base_sensitive mkw_retro_sensitive
     mkw_retro_rewind_functions WiiCompiled RetroRewind)
 foreach(target IN LISTS MKW_ALL_BUILD_TARGETS)
-    if(TARGET ${target})
-        target_compile_options(${target} PRIVATE -march=x86-64-v3)
+    if(TARGET ${target} AND MKW_BASELINE_ARCH_FLAG)
+        target_compile_options(${target} PRIVATE ${MKW_BASELINE_ARCH_FLAG})
     endif()
 endforeach()