Use -traditional with GNU cpp.

configure.in

@@ -2257,6 +2257,13 @@ changequote([, ])dnl
 echo creating src/epaths.h
 make epaths-force
 
+# As of 2000-11-19, newest development versions of GNU cpp preprocess
+# `..' to `. .'  unless invoked with -traditional
+
+if [ x$GCC = xyes && x$NON_GNU_CPP" = x ]; then
+  CPPFLAGS="$CPPFLAGS -traditional"
+fi
+
 echo creating lib-src/Makefile
 ( cd lib-src
   rm -f junk.c junk1.c junk2.c