I hope this helps . As noted in my comment, it is in fact a homebrew issue that it's not able to find the command line tools 'inside' Xcode due to Xcode recently changing where the command line tools were located... see these two issuesL github.com/Homebrew/homebrew/issues/24471 and github.com/Homebrew/homebrew/issues/20427 The solution was therefore to simply accept the option to install the command line tools when the gui window pops up after homebrew can't find them.
Running Jekyll on Mavericks with latest command line tools error
this one helps. You said that you are trying to use ruby 2.1.1. but your log show us ruby 1.8.7. With that in mind, it seems that you have 2 rubies installed on your machine... ruby 1.8.7 installed by homebrew, and ruby 2.1.1 installed by rvm.
gem uninstall jekyll
rvm use 2.1.1
gem install jekyll
Unable to use xcodebuild on Mavericks with Command Line Tools installed