fehler120: Backend discards float->int Conv for shift amount.

[r20772]

ir/be/test/fehler120.c

+/*$ -fno-inline $*/
+
+int f(float x)
+{
+	return 1 << (int)x;
+}
+
+int main(void)
+{
+	return f(3.0) != 8;
+}