[pangomm] Require C++17

[Murray Cumming <murrayc src gnome org>]

commit ba44b7c03e3a3d8242c1f0adf7c19b33e9cbf7a2
Author: Murray Cumming <murrayc murrayc com>
Date:   Sun Apr 8 22:08:30 2018 +0200

    Require C++17
    
    Because libsigc++-3.0 (and therefore glibmm) now requires C++17.

 configure.ac |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index d4549d8..795f64b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -32,7 +32,7 @@ m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 AM_MAINTAINER_MODE
 AC_ARG_VAR([ACLOCAL_FLAGS], [aclocal flags, e.g. -I <macro dir>])
 
-MM_PREREQ([0.9.10])
+MM_PREREQ([0.9.12])
 MM_INIT_MODULE([pangomm-2.42])
 
 # Copy the mm-common .pl scripts into docs/,
@@ -44,7 +44,7 @@ MM_CONFIG_DOCTOOL_DIR([docs])
 AC_SUBST([LIBPANGOMM_SO_VERSION], [1:30:0])
 
 AC_PROG_CXX
-MM_AX_CXX_COMPILE_STDCXX([14], [noext], [mandatory])
+MM_AX_CXX_COMPILE_STDCXX([17], [noext], [mandatory])
 
 AC_DISABLE_STATIC
 LT_INIT([win32-dll])