Several packages rely on the C pre-processor (xrdb among others). This package normally comes with the C compiler such as gcc. Sadly, in RedHat 5.2 only egcs provides /lib/cpp so that if you only install gcc, you won't get /lib/cpp nor any cpp manual. It seems that the conflict between egcs's cpp and gcc's cpp could be resolved in the same way as the conflict between csh's /bin/csh and tcsh's /bin/csh allowing both gcc and egcs to provide /lib/cpp and cpp's manual.
this is fixed in 5.9+ by having a separate cpp package.