[vte] build: Update macros from autoconf-archive

[Christian Persch <chpe src gnome org>]

commit 073a5600c11025660893a6558ae7db7bc9ecf874
Author: Christian Persch <chpe src gnome org>
Date:   Tue Mar 27 19:40:13 2018 +0200

    build: Update macros from autoconf-archive

 m4/ax_cxx_compile_stdcxx.m4 |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)
---
diff --git a/m4/ax_cxx_compile_stdcxx.m4 b/m4/ax_cxx_compile_stdcxx.m4
index 5032bba..85efc7c 100644
--- a/m4/ax_cxx_compile_stdcxx.m4
+++ b/m4/ax_cxx_compile_stdcxx.m4
@@ -40,12 +40,11 @@
 #   and this notice are preserved.  This file is offered as-is, without any
 #   warranty.
 
-#serial 7
+#serial 8
 
 dnl  This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
 dnl  (serial version number 13).
 
-AX_REQUIRE_DEFINED([AC_MSG_WARN])
 AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
   m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
         [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
@@ -139,7 +138,6 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
               [define if the compiler supports basic C++$1 syntax])
   fi
   AC_SUBST(HAVE_CXX$1)
-  m4_if([$1], [17], [AC_MSG_WARN([C++17 is not yet standardized, so the checks may change in incompatible 
ways anytime])])
 ])