Still failed, for not able to access gcc-4.6.2 automatically (have to access ~/gcc462/bin), I install binary GCC from HPC. So I'm extracted gcc-lion.tar.gz. For my surprise, it's extracted with some hierarchy like usr/local/bin, usr/local/include, … and I supposed to copy it to root folder. In that case, my Xcode4.2's gcc would still intact because it's in /usr/bin .

 I wonder if all gcc compilation result'll stored to /usr/local if we didn't pass any parameter, so I checked my /usr/local/bin directory

Nugrohos-MacBook-Pro:/ nugroho$ cd usr/local/bin/
Nugrohos-MacBook-Pro:bin nugroho$ ls
2to3gfortran                  python-config    smtpd.py
2to3-2.7    idle     python2.7    smtpd2.7.py
c++     idle2.7     python2.7-32    x86_64-apple-darwin11.2.0-c++
cpp     jcf-dump    python2.7-config   x86_64-apple-darwin11.2.0-g++
g++     pydoc     pythonw     x86_64-apple-darwin11.2.0-gcc
gcc     pydoc2.7    pythonw-32    x86_64-apple-darwin11.2.0-gcc-4.6.2
gcj     python     pythonw2.7    x86_64-apple-darwin11.2.0-gcj
gcov     python-32    pythonw2.7-32    x86_64-apple-darwin11.2.0-gfortran

There is gcc in it. Is in gcc-4.2?

Nugrohos-MacBook-Pro:bin nugroho$ ./gcc --version
gcc (GCC) 4.6.2
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Yes, it is gcc-4.6.2? So, I replace gcc symlink previously  pointed to /usr/bin/llvm-gcc to /usr/local/bin/gcc

Nugrohos-MacBook-Pro:bin nugroho$ which gcc
/usr/bin/gcc
Nugrohos-MacBook-Pro:bin nugroho$ which llvm-gcc
/usr/bin/llvm-gcc
Nugrohos-MacBook-Pro:bin nugroho$ sudo ln -s gc
gcc   gcj   gcov  
Nugrohos-MacBook-Pro:bin nugroho$ sudo ln -s gcc /usr/bin/gcc
Password:
ln: /usr/bin/gcc: File exists
Nugrohos-MacBook-Pro:bin nugroho$ sudo mv /usr/bin/gcc /usr/bin/gccOLD
Nugrohos-MacBook-Pro:bin nugroho$ sudo ln -s gcc /usr/bin/gcc
Nugrohos-MacBook-Pro:bin nugroho$ gcc
gcc: fatal error: no input files
compilation terminated.
Nugrohos-MacBook-Pro:bin nugroho$ gcc --version
gcc (GCC) 4.6.2
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Nugrohos-MacBook-Pro:bin nugroho$ 

Hooray, HPC binary is left untouched, :)