cmake: detect Cygwin which needs extensions to build
cmake: detect Cygwin which needs extensions to build

xnagireddy/googletest,xnagireddy/googletest,jlanecox/googletest,antidotcb/googletest,gianricardo/googletest,gianricardo/googletest,antidotcb/googletest,empiredan/googletest,google/googletest,empiredan/googletest,antidotcb/googletest,gianricardo/googletest,jlanecox/googletest,antidotcb/googletest,google/googletest,jlanecox/googletest,jlanecox/googletest,google/googletest,empiredan/googletest,google/googletest,xnagireddy/googletest,xnagireddy/googletest