[core] fixed undeclared SSE2 intrinsics on non-Win32

Source/Project64-core/N64System/N64Types.h

@@ -12,6 +12,17 @@
 
 #include <Common/stdtypes.h>
 
+/*
+ * The limits of COP1 extend to native SSE2 register capabilities, but for
+ * now this is only being included to dodge the MSVC inline asm for x86.
+ *
+ * As better cross-platform methods of handling FP precision are implemented
+ * for non-Intel-architecture builds, this #include may become obsolete.
+ */
+#if defined(__i386) || defined(__x86_64__) || defined(_M_X64)
+#include <emmintrin.h>
+#endif
+
 enum PauseType
 {
 	PauseType_FromMenu,