I got a full build to complete on both CentOS 6.7 and Fedora 22. However, the X.org binary built on Fedora 22 crashes as soon as I try to run pibox-network-config. The most likely cause of this is the changes I made to the toolchain, specifically the gcc compiler.
So I decided to go back to the old toolchain but built with the newer Crosstool-NG (1.22), but that doesn't support the exact gcc (4.7.3) I had used previously. So I tried the next closest one, 4.7.4. Unfortunately, Fedora 22 has gcc 5.x and that won't compile gcc older than 4.8 (re: 4.7.x and earlier) due to some bug. I lost the output I had and the link that told me this was the case, but I know it's a fact (that lost link had a patch for it). So I bumped up to gcc 4.8.5. That built and is now being used to rebuild the rest of the distribution, which I'll try as soon as the build completes.
If this does the same thing I'll revert to xcc 1.19.0 and try again.
Update:
Verified build is working on Fedora 22. Also verified that this build, with the 4.8.5 version of gcc, does not crash X.org when I start pibox-network-config.
More testing is necessary but I'm fairly confident this will be a working configuration for a while to come. At least the toolchain is.
Closing issue. Will open new issues against the new build as necessary.