re PR bootstrap/82856 (--enable-maintainter-mode broken by incompatiblity of gcc's required automake and modern Perl)

	PR bootstrap/82856

    libgo: update to autoconf 2.69 and automake 1.15.1
    
    Initial patch from Joseph Myers.
    
    Reviewed-on: https://go-review.googlesource.com/c/146417

From-SVN: r265701