Enable C++ in autoconf

acinclude.m4

@@ -55,6 +55,17 @@ if test "${ac_cv_c_compiler_gnu}" = "yes"; then
 fi # ac_cv_c_compiler_gnu
 ])
 
+# SANE_SET_AM_CXXFLAGS()
+# Set default AM_CXXFLAGS.
+AC_DEFUN([SANE_SET_AM_CXXFLAGS],
+[
+AX_CXX_COMPILE_STDCXX_11([noext], [mandatory])
+if test "${ac_cv_cxx_compiler_gnu}" = "yes"; then
+  AM_CXXFLAGS="$AM_CXXFLAGS -std=c++11"
+fi # ac_cv_cxx_compiler_gnu
+])
+
+
 dnl SANE_CHECK_MISSING_HEADERS
 dnl Do some sanity checks. It doesn't make sense to proceed if those headers
 dnl aren't present.

configure.ac

@@ -40,6 +40,7 @@ dnl ******************************************************************
 dnl  Set up the compiler and linker
 dnl ******************************************************************
 AC_PROG_CC
+AC_PROG_CXX
 AM_PROG_CC_C_O
 sane_save_CC=$CC
 AC_PROG_CC_C99                  dnl enables extensions to ISO C99 :-(
@@ -80,6 +81,7 @@ dnl ***********************************************************************
 dnl set compiler/linker flags
 dnl ***********************************************************************
 SANE_SET_AM_CFLAGS([$is_release])
+SANE_SET_AM_CXXFLAGS
 SANE_SET_AM_LDFLAGS
 
 dnl ***********************************************************************