Description of problem:
When debugging a user's problem on Fedora 15, I noticed the following strange error...

[root@fedora15-64-beta ~]# echo "#define _foo_\n" | gcc -E -
gcc: error trying to exec 'cc1': execvp: No such file or directory

The issue occurs because the user has a 64 bit gcc package installed but has a 32 bit cpp package installed.

[root@fedora15-64-beta ~]# rpm -qa | grep '^\(gcc\|cpp\)'
gcc-4.6.0-2.fc15.x86_64
cpp-4.6.0-2.fc15.i686

This is completely legitimate since the cpp dependency in the gcc package is not arch specific.

[root@fedora15-64-beta ~]# rpm -q gcc --requires | grep cpp
cpp = 4.6.0-2.fc15

So the solution is to make the dependency arch specific.

Version-Release number of selected component (if applicable):

gcc-4.6.0-2.fc15.x86_64
cpp-4.6.0-2.fc15.i686

How reproducible:
100%

Steps to Reproduce:
1. Install 32bit cpp package and 64 bit gcc package 
2. try and invoke the C pre-processor through GCC 
  
Actual results:
gcc: error trying to exec 'cc1': execvp: No such file or directory

Expected results:
pre-processed output.