Created attachment 319162 [details]
I've tried to install VirtualBox-4.1.18 and compilation failed every time.
Also I've tried to install 4.1.12 (stable version) with the following CFLAGS unsuccessfully:
1) -O1 -march=native -pipe -fomit-frame-pointer
2) -march=core2 -pipe
Created attachment 319164 [details]
It seems that the problem solved by switching to "i686-pc-linux-gnu-4.6.3-vanilla" gcc profile instead of "i686-pc-linux-gnu-4.6.3"
Created attachment 343018 [details]
emerge --info with the vanilla gcc profile.
I can confirm that the vanilla gcc profile resolved this issue (portage settings attached.)
This version has long been removed from portage.