Use simde as fallback simd implementation

include/simd-compat/mmintrin.h

@@ -21,6 +21,9 @@
 # include_next <mmintrin.h>
 #elif defined(__EMSCRIPTEN__)
 # include <wasm_simd128.h>
-#else
+#elif defined(__ARM_NEON)
 # include "../sse2neon/sse2neon.h"
+#else
+# define SIMDE_ENABLE_NATIVE_ALIASES
+# include <simde/x86/mmx.h>
 #endif

include/simd-compat/pmmintrin.h

@@ -29,7 +29,7 @@ __m64 _mm_set1_pi16(short w)
     return __extension__ (__m64){ static_cast<float>(w), static_cast<float>(w) };
 }
 
-#else
+#elif defined(__ARM_NEON)
 # include "../sse2neon/sse2neon.h"
 
 static inline
@@ -44,4 +44,10 @@ __m64 _mm_set1_pi16(short w)
     return vreinterpret_s64_s16(vdup_n_s16(w));
 }
 
+#else
+# define SIMDE_ENABLE_NATIVE_ALIASES
+# include <simde/x86/sse.h>
+# include <simde/x86/sse2.h>
+# include <simde/x86/sse3.h>
+
 #endif