kernel: optimize LcmInt for small inputs

This gives a tiny speed boost, but more importantly, avoids
unnecessary allocation of temporary memory

Before:

gap> for i in [1..10000000] do LcmInt(2^50*13, 2^50*17); od; time;
2605

After:

gap> for i in [1..10000000] do LcmInt(2^50*13, 2^50*17); od; time;
2427

src/integer.c

@@ -2202,6 +2202,15 @@ Obj LcmInt(Obj opL, Obj opR)
     sizeL = SIZE_INT_OR_INTOBJ(opL);
     sizeR = SIZE_INT_OR_INTOBJ(opR);
 
+    if (sizeL == 1 || sizeR == 1) {
+        if (sizeR != 1) {
+            SWAP(Obj, opL, opR);
+        }
+        Obj gcd = GcdInt(opL, opR);
+        opR = QuoInt(opR, gcd);
+        return AbsInt(ProdInt(opL, opR));
+    }
+
     NEW_FAKEMPZ(mpzResult, sizeL + sizeR);
     FAKEMPZ_GMPorINTOBJ(mpzL, opL);
     FAKEMPZ_GMPorINTOBJ(mpzR, opR);