tgamma function in math library

[Pierre Abbat <phma@xxxxxxxxxxxxx>]

I just copied one of my programming projects to the laptop and attempted to 
compile it. The compiler bombed out on the line:
 denom=tgamma(sh);
According to the man page for gamma on Linux:

   *BSD version
       4.4BSD and FreeBSD libm have a gamma() function that computes the Gamma
       function, as one would expect.

   glibc version
       Glibc has a gamma() function that is equivalent to  lgamma()  and  com‐
       putes  the  natural logarithm of the Gamma function.  (This is for com‐
       patibility reasons only.  Don’t use this function.)

How should I write the program so that it uses tgamma() on Linux and gamma() 
on DragonFly?

Pierre
-- 
La sal en el mar es más que en la sangre.
Le sel dans la mer est plus que dans le sang.