Use gcc version 4.7 instead of gcc 4.8

Several errors occurs with gcc 4.8.1 on 'hikirk' machines.

E.g. in most tests 'bonnie++' does not pass through.
root@hikirk:/media/test# bonnie++ -u 0
Using uid:0, gid:0.
Writing with putc()...done
Writing intelligently...done
Rewriting...done
Reading with getc()...done
Reading intelligently...done
start 'em...done...done...done...
Create files in sequential order...done.
Stat files in sequential order...Expected 16384 files but only got 16382
Cleaning up test directory after error.
Bonnie: drastic I/O error (rmdir): Directory not empty

Or unpack e.g. root-fs in a folder and delete the files immediately.
root@hikirk:/media/test# tar -xjf <rootfs.tar.bz2>
root@hikirk:/media/test# rm -rf *
rm: can't remove 'usr/share/terminfo/a/ansi+tabs': No such file or directory
rm: can't remove 'usr/share/terminfo/a': Directory not empty
rm: can't remove 'usr/share/terminfo': Directory not empty
rm: can't remove 'usr/share': Directory not empty
rm: can't remove 'usr': Directory not empty

The errors do not occur with gcc 4.7.2.

Signed-off-by: Mario Schuknecht <mario.schuknecht@dresearch-fe.de>