[Gentoo]Note that circular dependencies can often be avoided by temporarily

sun15 linux # emerge -pv gcc

These are the packages that would be merged, in order:

Calculating dependencies... done!


[nomerge      ] sys-devel/gcc-4.4.3 [4.1.1-r3] USE="fortran gtk mudflap nls nptl openmp (-altivec) -bootstrap -build -doc (-fixed-point) -gcj -graphite (-hardened) (-libffi) (-multilib) -multislot (-n32) (-n64) -nocxx -objc -objc++ -objc-gc -test -vanilla"
[ebuild     U ]  sys-libs/glibc-2.11-r1 [2.5-r4] USE="-gd% -vanilla%"
[ebuild  NS   ]   sys-devel/gcc-4.4.3 [4.1.1-r3] USE="fortran gtk mudflap nls nptl openmp (-altivec) -bootstrap -build -doc (-fixed-point) -gcj -graphite (-hardened) (-libffi) (-multilib) -multislot (-n32) (-n64) -nocxx -objc -objc++ -objc-gc -test -vanilla"

 * Error: circular dependencies:

('ebuild', '/', 'sys-libs/glibc-2.11-r1', 'merge') depends on
  ('ebuild', '/', 'sys-devel/gcc-4.4.3', 'merge') (hard)
('ebuild', '/', 'sys-devel/gcc-4.4.3', 'merge') depends on
  ('ebuild', '/', 'sys-libs/glibc-2.11-r1', 'merge') (hard)

 * Note that circular dependencies can often be avoided by temporarily
 * disabling USE flags that trigger optional dependencies.
emerge --oneshot --nodeps -pv gcc

emerge -a gcc

http://en.gentoo-wiki.com/wiki/Circular_dependencies