Add all the effects of 'cygnus' for which there exists an explicit way
to request that behaviour:
* Implied foreign strictness and options no-installinfo, no-dependencies
and no-dist are added to AM_INIT_AUTOMAKE in newlib/acinclude.m4.
* macro AM_MAINTAINER_MODE is added to newlib/acinclude.m4.
* For the implied TEXINFO_TEX of '$(top_srcdir)/../texinfo/texinfo.tex',
an explicit TEXINFO_TEX is always relative to $(srcdir), so write the
same pathname in that form.
This is to prepare for the removal of the automake option '--cygnus'.
320510de2c