configure: Check whether we need to link against -lm
configure: Check whether we need to link against -lm

This adds a check for whether the math library functions are
accessible without -lm. If not autoconf will add libm to the linker
flags.

eliasbakken/mash,eliasbakken/mash,clutter-project/mash,clutter-project/mash,clutter-project/mash