Description of problem:
Attempting to rebuild gcc-python-plugin, I ran into this issue on ppc64 and ppc64le:


checking for gcc-plugin.h... not found
Test compilation failed with exit code 1
  The command was:
    gcc -c -o config-tests/00001-checking-for-gcc-plugin.h/feature-test.o -I/usr/lib/gcc/ppc64le-redhat-linux/8/plugin/include -x c++ config-tests/00001-checking-for-gcc-plugin.h/feature-test.c
  The source was: (in config-tests/00001-checking-for-gcc-plugin.h/feature-test.c)
    #include <gcc-plugin.h>
  The stderr was:
    In file included from /usr/lib/gcc/ppc64le-redhat-linux/8/plugin/include/tm.h:26,
                     from /usr/lib/gcc/ppc64le-redhat-linux/8/plugin/include/backend.h:28,
                     from /usr/lib/gcc/ppc64le-redhat-linux/8/plugin/include/gcc-plugin.h:30,
                     from config-tests/00001-checking-for-gcc-plugin.h/feature-test.c:1:
    /usr/lib/gcc/ppc64le-redhat-linux/8/plugin/include/config/rs6000/rs6000.h:35:10: fatal error: config/rs6000/rs6000-modes.h: No such file or directory
     #include "config/rs6000/rs6000-modes.h"
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    compilation terminated.
make: *** [Makefile:177: autogenerated-config.h] Error 1

I'm guessing it's an unpackaged header file.

Failed build on ppc64le:
  https://koji.fedoraproject.org/koji/taskinfo?taskID=27927700
and on ppc64:
  https://koji.fedoraproject.org/koji/taskinfo?taskID=27927702

Version-Release number of selected component (if applicable):
gcc-plugin-devel.ppc64 8.1.1-3.fc29
gcc-plugin-devel.ppc64le 8.1.1-3.fc29