got this error when trying to autogen 1.9 branch.
Vector said he had the same problem on linux but apt-search was able to the real name go gnet-2.0 and he just installed it.
I trawled thru cygwin pacakges but couldnt find it
Package gnet-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gnet-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gnet-2.0' found
configure: error: Cannot find GNet: Is gnet-config in path?