avoid to use std::ceil

[mdionisio]

avoid to used "ceil" has the good collateral effect that math library is not used any more and if we build libzmq with statically linked stdc++ we can avoid to add "-lm"

[bluca]

Can you remove the -lm given it's no longer necessary? Also please fix the indentation:

-    _max_counters (
-      (_max_size + msg_t::max_vsm_size - 1)
-      / msg_t::max_vsm_size)
+    _max_counters ((_max_size + msg_t::max_vsm_size - 1) / msg_t::max_vsm_size)

[mdionisio]

I will fix the indentation, but I cannot remove the "-lm" because it is an implicit dependency of libstdc++