[R-SIG-Mac] Which command line tools for XCode 4.2.1

[cstrato]

Dear Simon,

On your developer site you mention:
"We use Xcode 4.2 but Xcode 3.2 and higher should work as well. Note 
that you will need Command Line Tools component of Xcode on Mac OS X 
10.7 or higher."

I am running OS X 10.7.5 and XCode 4.2.1 on my Mac, but have not 
downloaded the command line tools. My questions are:

- why do I need the command line tools?

- which version do I need to download from:
https://developer.apple.com/downloads/index.action

There are e.g.
   - Command Line Tools (OS X Lion) for Xcode - October 2012
     (it is not mentioned which version of Xcode)
   - Command Line Tools (OS X Lion) for Xcode - November 2012
     (Xcode 4.3 is mentioned but it is nor clear if it works with 4.2.1)
   - Command Line Tools (OS X Lion) for Xcode - April 2013
     (Xcode 4.6.2 is mentioned but it is nor clear if it works with 4.2.1)

   (BTW, the Preferences for Xcode 4.2.1 do not list Command Line Tools 
in the Install window.)

- do the Command Line Tools update clang/clang++?

The reason for my question is that in order to compile the C++ code in 
my package with clang I need at least version 3.1 since 3.0 results in 
an error.

Best regards,
Christian