Valgrind does currently not build in mock in x86_64. The error is as follows: /usr/include/gnu/stubs.h:7:27: error: gnu/stubs-32.h: No such file or directory This is part of glibc-devel.i386, which is not installed in mock builds. The x86_64 glibc-devel only supplies stubs-64.h. Is this requirement on the ia32 headerfile really needed?
mock is incapable of handling multilib builds, but that's something that needs to be fixed in mock, not the individual packages. At least gcc, compat-gcc-32 and valgrind need glibc{,-devel} for the other arch installed.
Should be fixed in valgrind-3.1.1-3 the same way as gcc requires this now. The rest is mock bug.