AM_C_PROTOTYPES is no longer supported.

https://lists.gnu.org/archive/html/automake-patches/2011-06/msg00082.html

Failure without patch:

starting phase `autoreconf'
aclocal: warning: autoconf input should be named 'configure.ac', not 'configure.in'
configure.in:11: error: automatic de-ANSI-fication support has been removed
/gnu/store/…-automake-1.15/share/aclocal-1.15/obsolete.m4:26: AM_C_PROTOTYPES is expanded from...
configure.in:11: the top level


Upstream is dead.
--- a/configure.in	2015-03-15 18:59:12.557417149 +0100
+++ b/configure.in	2015-03-15 18:59:29.273416518 +0100
@@ -8,7 +8,6 @@
 AC_PROG_CC
 AC_PROG_CXX
 AC_ISC_POSIX
-AM_C_PROTOTYPES
 if test "x$U" != "x"; then
   AC_MSG_ERROR(Compiler not ANSI compliant)
 fi