emitter: Remove pointer casts

This should also technically silence quite a few ubsan warnings.

src/common/x64/emitter.h

@@ -359,10 +359,10 @@ private:
     void ABI_CalculateFrameSize(u32 mask, size_t rsp_alignment, size_t needed_frame_size, size_t* shadowp, size_t* subtractionp, size_t* xmm_offsetp);
 
 protected:
-    void Write8(u8 value)   {*code++ = value;}
-    void Write16(u16 value) {*(u16*)code = (value); code += 2;}
-    void Write32(u32 value) {*(u32*)code = (value); code += 4;}
-    void Write64(u64 value) {*(u64*)code = (value); code += 8;}
+    void Write8(u8 value);
+    void Write16(u16 value);
+    void Write32(u32 value);
+    void Write64(u64 value);
 
 public:
     XEmitter() { code = nullptr; flags_locked = false; }