tgamma
#define tgamma(x) __tg_simple(x, tgamma)
y = tgamma(y);
y = - x * tgamma(-x);
__weak_reference(tgamma, tgammal);
double tgamma(double);
return (tgamma(x));
TGMACRO_REAL(tgamma)
PASS_REAL_ARG_REAL_RET(tgamma));