Immediately after GCC 4.8.0 was released, I built it on OS X 10.8 with ISL and CLooG. The complete build was about 3.8 GB in size (release tar balls + untarred sources + all generated objects). I couldn't remember which compiler I used for that build. I guess GCC does not pick up Apple clang? Then probably the compiler was the default GCC 4.2.1 /usr/bin; all other versions of GCC were installed elsewhere, and I'm sure I didn't customize CC.
Today I built GCC 4.8.0 again on Ubuntu 12.04, this time without ISL and CLooG. The complete build was about 5.3 GB in size (still release tar balls + untarred sources + all generated objects). The compiler for this build was GCC 4.7.3.
This is rather interesting. Why are the sizes so much different? Does this indicate that Mach-O is more space-efficient than ELF? Or are there other factors?