Short Answer:
I needed the native (i.e for CentOS) GCC tools to build and run gen-fac_ui.
Long Answer: This is my post at the OSDev forum, where I basically asked the same question and got an answer. It also contains my error (and correction) of not having glibc-devel installed for the native GCC toolchain.
In addition, since the base version of GCC for my build system was 4.4.7 and I was trying to cross-native build 4.7, I had to get the developer toolset, which can be installed via yum. Information on the toolset is here and easy install instructions are here
FWIW, I'm still not entirely sure how I was supposed to determine that gen-fac_ui needed to be made by a gcc native to the build machine...other than there was no other way I could find to generate fac_ui.h and other headers.