# emerge -C =sys-devel/gcc-4.7.3-r1
 * This action can remove important packages! In order to be safer, use
 * `emerge -pv --depclean <atom>` to check for reverse dependencies before
 * removing packages.

 sys-devel/gcc
    selected: 4.7.3-r1 
   protected: none
     omitted: 4.8.3 

All selected packages: =sys-devel/gcc-4.7.3-r1

>>> 'Selected' packages are slated for removal.
>>> 'Protected' and 'omitted' packages will not be removed.

>>> Waiting 5 seconds before starting...
>>> (Control-C to abort)...
>>> Unmerging in: 5 4 3 2 1
>>> Unmerging (1 of 1) sys-devel/gcc-4.7.3-r1...
 * Switching native-compiler to x86_64-pc-linux-gnu-4.8.4 ...>>> Regenerating
 * /etc/ld.so.cache...
 [ ok ]
 * Running 'fix_libtool_files.sh 4.7.3'
Scanning libtool files for hardcoded gcc library paths...
 *   [1/14] Scanning /lib ...
 *   [2/14] Scanning /usr/lib ...
 *   [3/14] Scanning /lib32 ...
 *   [4/14] Scanning /lib64 ...
 *   [5/14] Scanning /usr/games/lib ...
 *   [6/14] Scanning /usr/games/lib32 ...
 *   [7/14] Scanning /usr/games/lib64 ...
 *   [8/14] Scanning /usr/lib32 ...
 *   [9/14] Scanning /usr/lib64 ...
 *   [10/14] Scanning /usr/local/lib ...
 *   [11/14] Scanning /usr/local/lib32 ...
 *   [12/14] Scanning /usr/local/lib64 ...
 *   [13/14] Scanning /opt/picoscope/lib ...
 *   [14/14] Scanning /usr/x86_64-pc-linux-gnu/lib ...

although fix_libtool_files on its own is no issue:
# fix_libtool_files.sh 4.7.3
Scanning libtool files for hardcoded gcc library paths...
 *   [1/14] Scanning /lib ...
 *   [2/14] Scanning /usr/lib ...
 *   [3/14] Scanning /lib32 ...
 *   [4/14] Scanning /lib64 ...
 *   [5/14] Scanning /usr/games/lib ...
 *   [6/14] Scanning /usr/games/lib32 ...
 *   [7/14] Scanning /usr/games/lib64 ...
 *   [8/14] Scanning /usr/lib32 ...
 *   [9/14] Scanning /usr/lib64 ...
 *   [10/14] Scanning /usr/local/lib ...
 *   [11/14] Scanning /usr/local/lib32 ...
 *   [12/14] Scanning /usr/local/lib64 ...
 *   [13/14] Scanning /opt/picoscope/lib ...
 *   [14/14] Scanning /usr/x86_64-pc-linux-gnu/lib ...

# echo $?
0

Although it is using 4.8.4 and omitting 4.8.3, this is due to improperly
registered 4.8.4 after a hang during install. As seen in gcc-config
4.8.3 is actually not selectable

# gcc-config -l
[1] i686-w64-mingw32-4.7.3 *

[2] x86_64-pc-linux-gnu-4.8.4 *