libint2-debuginfo 2.0.2-1.615hg does not contain sources. The build log is 358M which will take a long time to download from the slow koji servers so I'll leave finding out why this is to you ($RPM_OPT_FLAGS not being used somewhere where it should, premature stripping or something...?)
Opflags *are* used in the build, my guess is that since the library sources are autogenerated by the compiler, normal debuginfo stuff just doesn't work. There seem to be 1.9GB worth of source files in the build tree.
The problem was indeed solved by pregenerating the sources.