#19 PPTPD build system is incompatible with >=automake-1.13

[Sergey Popov]

PPTPD failed to compile with automake 1.13, resulting in errors:

aclocal-1.13: warning: autoconf input should be named 'configure.ac', not 'configure.in'
configure.in:3: error: 'AM_CONFIG_HEADER': this macro is obsolete.
You should use the 'AC_CONFIG_HEADERS' macro instead.
/usr/share/aclocal-1.13/obsolete-err.m4:12: AM_CONFIG_HEADER is expanded from...
configure.in:3: the top level
autom4te-2.69: /usr/bin/m4 failed with exit status: 1
aclocal-1.13: error: echo failed with exit status: 1

Draft patch attached, downstream bugreport: https://bugs.gentoo.org/show_bug.cgi?id=469476

[James Cameron]

Please revalidate against pptpd-1.5.0