lgamma non-standard extension

[coypu%sdf.org@localhost]

hi folks,

we have a small compatible extension to lgamma, a standard C function.
we provide the sign of gamma(x) result in signgam, in a global.

we also have a reentry safe version, lgamma_r, where signgam is passed
as an argument.

because this is a standard C function, I assume the compiler is
completely free to replace it with a standard implementation, so using
our extension is unsafe even on netbsd.

i think it would be reasonable to get rid of the extension (modifying
signgam) in the next shlib major bump for this reason.

thoughts?

secondary: would we want to keep lgamma_r then?