gcd: Add more tests that require few more divisions

@colincross identified gcd does not have a single case whose answer is not 0, 1, or the smaller of the two inputs.

Author: hiraditya

libcxx/test/std/numerics/numeric.ops/numeric.ops.gcd/gcd.pass.cpp

@@ -27,7 +27,7 @@ constexpr struct {
   int x;
   int y;
   int expect;
-} Cases[] = {{0, 0, 0}, {1, 0, 1}, {0, 1, 1}, {1, 1, 1}, {2, 3, 1}, {2, 4, 2}, {11, 9, 1}, {36, 17, 1}, {36, 18, 18}};
+} Cases[] = {{0, 0, 0}, {1, 0, 1}, {0, 1, 1}, {1, 1, 1}, {2, 3, 1}, {2, 4, 2}, {11, 9, 1}, {36, 17, 1}, {36, 18, 18}, {25, 30, 5}, {24, 16, 8}, {256, 100, 4}};
 
 template <typename Input1, typename Input2, typename Output>
 constexpr bool test0(int in1, int in2, int out)