can't find ceil function in math library

[Minxuan Zhuang]

hi：

I have a configure.ac file includes:  AC_CHECK_LIB([m], [ceil]) 

then I got this result: checking for ceil in -lm... no

but a .c file contains ceil function works very well  with or without -lm, why is that?

libtool version: 2.4.2

system： Ubuntu 13.04