#1 library uses libm but doesn't links against it

[Cristian Morales Vega]

-lm should be added to $LIBS. Works because other libs already do, but libass should link directly to it.
I don't submit a patch because I know -lm is needed in Linux, but I don't know if the functions are in libc or anything else in other systems.

[Nobody/Anonymous]

You are right, libm should be added to the linker flags. So far it only works by accident; either because of one of the included library's dependencies or because of gcc, which has builtins for most libm functions. I added a check to the configure script.