Since app-text/pdftk depends on sys-devel/gcc[gcj], emerging pdftk causes gcc to be downgraded to the latest version whose ebuild offers the gcj use flag. For instance:

1. emerge -pvt app-text/pdftk

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

Calculating dependencies... done!
[ebuild N ] app-text/pdftk-2.02 0 kB
[ebuild UD ] sys-devel/gcc-4.6.2-r1:4.6 [4.6.4-r2:4.6] USE="cxx doc fortran gcj%* gtk%* mudflap%* (multilib) nls nptl objc objc++ objc-gc%* openmp (-altivec) (-fixed-point) -graphite% (-hardened) (-libssp) -multislot -nopie% -nossp% {-test%} -vanilla (-ada%) (-f77%) (-f95%)" 0 kB

Total: 2 packages (1 downgrade, 1 new), Size of downloads: 0 kB