Segfault generating src/post_modules/GL/auto.c on PowerPC

[Marcus Comstedt (ACROSS) (Hail Ilpalazzo!) @ Pike (-) developers forum]

With some "handpåläggning" I managed to build exactly the SVN snapshot
of gcc 6.3-pre that was supposed to exhibit the problem (r241817).
However, Pike 8.0 (ad9b4ef) builds fine, and passes make verify as
well.  The plot thickens...  I guess I'll try specifying your exact
list of configure options next.