Removed an example of -DCMAKE_C_FLAGS=-g3 from the doc because it will become the default
Removed an example of -DCMAKE_C_FLAGS=-g3 from the doc because it will become the default

yannick/h2o,yannick/h2o,cwyang/h2o,yannick/h2o,devnexen/h2o,cwyang/h2o,devnexen/h2o,h2o/h2o,h2o/h2o,h2o/h2o,h2o/h2o,yannick/h2o,yannick/h2o,cwyang/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,cwyang/h2o,h2o/h2o,cwyang/h2o,devnexen/h2o,yannick/h2o,h2o/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,cwyang/h2o,yannick/h2o,devnexen/h2o,cwyang/h2o,h2o/h2o,cwyang/h2o