Include config.h in MIN-CPPFLAGS

This is needed when processing the Versions files since they could
refer to macros defined in config.h.  config.h was earlier included
through libc-symbols.h but since MIN-CPPFLAGS does not include the
latter anymore, it needs to at least include config.h.

This was causing a difference in generated code on s390x.  With this
change, s390x code is also unchanged with this and other 19 patches
(barring the IN_LIB patch of course).

	* Makeconfig (MIN-CPPFLAGS): Include config.h.