Clang and GCC 9 work fine

build/autotools/configure.ac

@@ -16,7 +16,7 @@ EGG_SAVE_PARAMETERS
 dnl Search for newer gcc versions before older
 #AC_REQUIRE_CPP
 AC_LANG([C++])
-AC_PROG_CXX([clang++80 clang++70 clang++60 clang++50 clang++40 clang++39 clang++38 clang++37 clang++36 clang++35 clang++34 g++8 g++7 g++6 g++5 clang++ eg++ g++ c++ CC cxx cc++])
+AC_PROG_CXX([clang++90 clang++80 clang++70 clang++60 clang++50 clang++40 clang++39 clang++38 clang++37 clang++36 clang++35 clang++34 g++9 g++8 g++7 g++6 g++5 clang++ eg++ g++ c++ CC cxx cc++])
 CC="${CXX} -x c"
 AC_SUBST(CC)
 AC_REQUIRE_CPP

configure

@@ -2512,7 +2512,7 @@ if test -z "$CXX"; then
     CXX=$CCC
   else
     if test -n "$ac_tool_prefix"; then
-  for ac_prog in clang++80 clang++70 clang++60 clang++50 clang++40 clang++39 clang++38 clang++37 clang++36 clang++35 clang++34 g++8 g++7 g++6 g++5 clang++ eg++ g++ c++ CC cxx cc++
+  for ac_prog in clang++90 clang++80 clang++70 clang++60 clang++50 clang++40 clang++39 clang++38 clang++37 clang++36 clang++35 clang++34 g++9 g++8 g++7 g++6 g++5 clang++ eg++ g++ c++ CC cxx cc++
   do
     # Extract the first word of "$ac_tool_prefix$ac_prog", so it can be a program name with args.
 set dummy $ac_tool_prefix$ac_prog; ac_word=$2
@@ -2556,7 +2556,7 @@ fi
 fi
 if test -z "$CXX"; then
   ac_ct_CXX=$CXX
-  for ac_prog in clang++80 clang++70 clang++60 clang++50 clang++40 clang++39 clang++38 clang++37 clang++36 clang++35 clang++34 g++8 g++7 g++6 g++5 clang++ eg++ g++ c++ CC cxx cc++
+  for ac_prog in clang++90 clang++80 clang++70 clang++60 clang++50 clang++40 clang++39 clang++38 clang++37 clang++36 clang++35 clang++34 g++9 g++8 g++7 g++6 g++5 clang++ eg++ g++ c++ CC cxx cc++
 do
   # Extract the first word of "$ac_prog", so it can be a program name with args.
 set dummy $ac_prog; ac_word=$2