compiler: Fix emitting big uint64 constants

Currently we take int64 value from the Go parser and push it to the
stack. Using uint64 is not a common practice (usually we just use `int`),
but can be a problem while doing bit arithmetic and serializing numbers.

Signed-off-by: Evgenii Stratonikov <fyfyrchik@runbox.com>

pkg/compiler/numeric_test.go

@@ -18,6 +18,14 @@ var numericTestCases = []testCase{
 		`,
 		big.NewInt(6),
 	},
+	{
+		"shift uint64",
+		`package foo
+		func Main() uint64 {
+			return 1 << 63
+		}`,
+		new(big.Int).SetUint64(1 << 63),
+	},
 }
 
 func TestNumericExprs(t *testing.T) {