Hostboot fails to build on Debian Stretch ppc64el

[madscientist159]

Trying to build hostboot as part of op-build on Debian Stretch ppc64el fails with:

Cannot open: ../../../../src/include/usr/tracinterface.H: No such file or directory at ./genErrlParsers.pl line 462.
makefile:79: recipe for target 'gen_errl_parsers' failed
make[9]: *** [gen_errl_parsers] Error 2

[madscientist159]

This was traced to buildroot corrupting symlinks inside hostboot. Pull request at open-power/buildroot#24