feat(asm): encode the amd64 system, string and segment families

The no-operand flag and system controls, the sign-extension pair, the
string primitives, the multi-byte no-ops, the cache controls, MOVBE, the
compare-exchange doubles, the random source and FS/GS base pairs, the
descriptor-table accesses, the 0F 00/01 register controls and the
LAR/LSL selector reads and far-segment loads, each pinned byte for byte
against go tool asm through every corpus line the toolchain's own
amd64enc.s carries for the families (279 lines).

Assisted-by: GLM 5.3 Flash

asm/amd64_families.go

@@ -11,6 +11,9 @@ func (e *enc) encodeAmd64Family(upper string, ops []Operand) (bool, error) {
 	if ok, err := e.encodeX87(upper, ops); ok {
 		return true, err
 	}
+	if ok, err := e.encodeSystem(upper, ops); ok {
+		return true, err
+	}
 	return false, nil
 }
 
@@ -36,5 +39,49 @@ func amd64FamilyEncodable(upper string) bool {
 	if _, ok := x87Fxsav[upper]; ok {
 		return true
 	}
-	return upper == "FADDDP"
+	if upper == "FADDDP" {
+		return true
+	}
+	if _, ok := systemNoOperand[upper]; ok {
+		return true
+	}
+	if b, size := splitSize(upper); size != 0 {
+		switch upper[len(upper)-1] {
+		case 'B', 'W', 'L', 'Q':
+			if _, ok := stringOp[b]; ok {
+				return true
+			}
+		}
+		if m, ok := sysRm[b]; ok && m.sized {
+			return true
+		}
+	}
+	if _, ok := nopWidth[upper]; ok {
+		return true
+	}
+	if _, ok := cacheControl[upper]; ok {
+		return true
+	}
+	if _, ok := movbeSize[upper]; ok {
+		return true
+	}
+	if _, ok := randSource[base(upper, 6)]; ok {
+		return true
+	}
+	if _, ok := fsGsBase[base(upper, 8)]; ok {
+		return true
+	}
+	if _, ok := descTable[upper]; ok {
+		return true
+	}
+	if _, ok := sysRm[upper]; ok {
+		return true
+	}
+	if _, ok := selectorRead[base(upper, 3)]; ok {
+		return true
+	}
+	if _, ok := farSegLoad[base(upper, 3)]; ok {
+		return true
+	}
+	return upper == "CMPXCHG8B" || upper == "CMPXCHG16B"
 }