Evaluate an complementary incomplete gamma function:
$$\gamma^{*}(a, x) = \int_{x}^{\infty} t^{a-1} e^{-t}dt,$$
using SLATEC dgamic in https://netlib.org/slatec/.
When (\(x > 0\) and \(a \ge 0\)) or (\(x \ge 0\) and \(a > 0\)),
compute the result, otherwise the value is NaN.