[gegl] configure.ac: require C++14 for C++ operations

[Ell <ell src gnome org>]

commit 5367ba6c579228848b72d7df0c08d482a75d15de
Author: Ell <ell_se yahoo com>
Date:   Sun Nov 25 15:54:22 2018 -0500

    configure.ac: require C++14 for C++ operations
    
    Bump the required C++ version to build C++ operations to C++14,
    which is required by gegl:voronoi-diagram since the last commit, in
    order to use polymorphic lambdas.

 configure.ac                    | 14 +++++++-------
 operations/Makefile.am          |  2 +-
 operations/workshop/Makefile.am |  2 +-
 3 files changed, 9 insertions(+), 9 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 785829ead..0bfb83bdc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -208,13 +208,13 @@ case "$CXX" in
     ;;
 esac
 
-dnl C++11 support
-have_cxx11="no"
-AX_CXX_COMPILE_STDCXX([11], , [optional])
-if test "x$HAVE_CXX11" = "x1"; then
-  have_cxx11="yes"
+dnl C++14 support
+have_cxx14="no"
+AX_CXX_COMPILE_STDCXX([14], , [optional])
+if test "x$HAVE_CXX14" = "x1"; then
+  have_cxx14="yes"
 fi
-AM_CONDITIONAL(HAVE_CXX11, test "x$have_cxx11" = "xyes")
+AM_CONDITIONAL(HAVE_CXX14, test "x$have_cxx14" = "xyes")
 
 dnl Large file support.
 AC_SYS_LARGEFILE
@@ -1367,7 +1367,7 @@ Optional features:
   Build website:   $have_asciidoc
   SIMD:            sse:$enable_sse mmx:$enable_mmx
   Vala support:    $have_vala
-  C++11:           $have_cxx11
+  C++14:           $have_cxx14
 
 Optional dependencies:
   asciidoc:        $have_asciidoc
diff --git a/operations/Makefile.am b/operations/Makefile.am
index 9ceadceda..45d98e051 100644
--- a/operations/Makefile.am
+++ b/operations/Makefile.am
@@ -1,4 +1,4 @@
-if HAVE_CXX11
+if HAVE_CXX14
 common_cxx = common-cxx
 endif
 
diff --git a/operations/workshop/Makefile.am b/operations/workshop/Makefile.am
index 75c7de4e8..b1985416d 100644
--- a/operations/workshop/Makefile.am
+++ b/operations/workshop/Makefile.am
@@ -27,7 +27,7 @@ ops = \
        segment-kmeans.la \
        selective-hue-saturation.la
 
-if HAVE_CXX11
+if HAVE_CXX14
 
 voronoi_diagram_la_SOURCES = voronoi-diagram.cc