externals: Update Xbyak to v5.51

Xbyak now supports multi-byte nops

externals/xbyak

@@ -1 +1 @@
-Subproject commit d62f6fb28f3c7b3fafb201b2ce65b653b547659c
+Subproject commit b633c68b53654154699e2780449c47d3049c4420

src/backend_x64/block_of_code.cpp

@@ -207,45 +207,6 @@ void BlockOfCode::SwitchToNearCode() {
     SetCodePtr(near_code_ptr);
 }
 
-void BlockOfCode::nop(size_t size) {
-    switch (size) {
-    case 0:
-        return;
-    case 1:
-        db(0x90);
-        return;
-    case 2:
-        db(0x66); db(0x90);
-        return;
-    case 3:
-        db(0x0f); db(0x1f); db(0x00);
-        return;
-    case 4:
-        db(0x0f); db(0x1f); db(0x40); db(0x00);
-        return;
-    case 5:
-        db(0x0f); db(0x1f); db(0x44); db(0x00); db(0x00);
-        return;
-    case 6:
-        db(0x66); db(0x0f); db(0x1f); db(0x44); db(0x00); db(0x00);
-        return;
-    case 7:
-        db(0x0f); db(0x1f); db(0x80); db(0x00); db(0x00); db(0x00); db(0x00);
-        return;
-    case 8:
-        db(0x0f); db(0x1f); db(0x84); db(0x00); db(0x00); db(0x00); db(0x00); db(0x00);
-        return;
-    case 9:
-        db(0x66); db(0x0f); db(0x1f); db(0x84); db(0x00); db(0x00); db(0x00); db(0x00); db(0x00);
-        return;
-    case 10:
-    default:
-        db(0x66); db(0x2e); db(0x0f); db(0x1f); db(0x84); db(0x00); db(0x00); db(0x00); db(0x00); db(0x00);
-        nop(size - 10);
-        return;
-    }
-}
-
 void* BlockOfCode::AllocateFromCodeSpace(size_t alloc_size) {
     if (size_ + alloc_size >= maxSize_) {
         throw Xbyak::Error(Xbyak::ERR_CODE_IS_TOO_BIG);

src/backend_x64/block_of_code.h

@@ -103,7 +103,6 @@ public:
     }
 
     void int3() { db(0xCC); }
-    void nop(size_t size = 1);
 
     /// Allocate memory of `size` bytes from the same block of memory the code is in.
     /// This is useful for objects that need to be placed close to or within code.