[Premake] Remove AVX2 requirement from linux build

Co-authored-by: has207 <429230+has207@users.noreply.github.com>

premake5.lua

@@ -126,7 +126,7 @@ filter({"configurations:Release", "platforms:Windows"}) -- "toolset:msc"
 filter("platforms:Linux")
   system("linux")
   toolset("clang")
-  vectorextensions("AVX2")
+  vectorextensions("AVX")
   --buildoptions({
   --    "-mlzcnt",   -- (don't) Assume lzcnt is supported.
   --})

src/xenia/base/memory.cc

@@ -308,6 +308,11 @@ void copy_and_swap_32_aligned(void* dest_ptr, const void* src_ptr,
   }
 }
 
+// Enable AVX2 for this function even when building with -mavx
+// The function has runtime detection to only use AVX2 on supported CPUs
+#if defined(__GNUC__) || defined(__clang__)
+__attribute__((target("avx2")))
+#endif
 void copy_and_swap_32_unaligned(void* dest_ptr, const void* src_ptr,
                                 size_t count) {
   auto dest = reinterpret_cast<uint32_t*>(dest_ptr);