llvm-3.1, installation, command execution failed

[annelyse.thevenin@…]

I am in Moutain Lion (since few days), I am a beginner in mac. I want to install some ports (R, gcc, ...) which need llvm-3.1.

The first time I wanted to install llvm-3.1 (directly or by the installation of R) I had this message:

Error: No valid Xcode installation is properly selected.
Error: Please use xcode-select to select an Xcode installation:
Error:     sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer # version 

After check if "/Applications/Xcode.app/Contents/Developer" exists, I write the sudo command suggested.

But I have an other message error (after sudo port clean llvm-3.1 and sudo port install llvm-3.1):

[...]
--->  Building llvm-3.1
Error: org.macports.build for port llvm-3.1 returned: command execution failed
Please see the log file for port llvm-3.1 for details:
/opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_llvm-3.1/llvm-3.1/main.log
To report a bug, follow the instructions in the guide:
    http://guide.macports.org/#project.tickets
Error: Processing of port llvm-3.1 failed

I put the main.log file in attachment.

Like suggested in ​https://trac.macports.org/wiki/ProblemHotlist#compiler I tried with foo=llvm-3.1:

sudo port clean foo
sudo port install foo configure.compiler=llvm-gcc-4.2

then

sudo port clean foo
sudo port install apple-gcc42
sudo port install foo configure.compiler=apple-gcc-4.2

It is doesn't work.

Could you help me?