Don't taint CXXFLAGS from AX_CXX_COMPILE_STDCXX_11

configure.ac

@@ -189,10 +189,20 @@ else
 d])
 fi
 
+ac_save_CXXFLAGS="$CXXFLAGS"
+CXXFLAGS=
+
 AX_CXX_COMPILE_STDCXX_11([noext], [optional])
 
+CXX1XCXXFLAGS="$CXXFLAGS"
+CXXFLAGS="$ac_save_CXXFLAGS"
+AC_SUBST([CXX1XCXXFLAGS])
+
 AC_LANG_PUSH(C++)
 
+ac_save_CXXFLAGS="$CXXFLAGS"
+CXXFLAGS="$CXXFLAGS $CXX1XCXXFLAGS"
+
 # Check that std::future is available.
 AC_MSG_CHECKING([whether std::future is available])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
@@ -226,6 +236,8 @@ std::map<int, int>().emplace(1, 2);
     [have_std_map_emplace=no
      AC_MSG_RESULT([no])])
 
+CXXFLAGS=$ac_save_CXXFLAGS
+
 AC_LANG_POP()
 
 # Checks for libraries.
@@ -797,6 +809,7 @@ AC_MSG_NOTICE([summary of build options:
       C preprocessor: ${CPP}
       CPPFLAGS:       ${CPPFLAGS}
       WARNCFLAGS:     ${WARNCFLAGS}
+      CXX1XCXXFLAGS:  ${CXX1XCXXFLAGS}
       EXTRACFLAG:     ${EXTRACFLAG}
       LIBS:           ${LIBS}
     Library:

examples/Makefile.am

@@ -24,7 +24,7 @@
 if ENABLE_EXAMPLES
 
 AM_CFLAGS = $(WARNCFLAGS)
-AM_CXXFLAGS = $(WARNCXXFLAGS)
+AM_CXXFLAGS = $(WARNCXXFLAGS) $(CXX1XCXXFLAGS)
 AM_CPPFLAGS = \
 	-I$(top_srcdir)/lib/includes \
 	-I$(top_builddir)/lib/includes \

src/Makefile.am

@@ -27,7 +27,7 @@ check_PROGRAMS =
 TESTS =
 
 AM_CFLAGS = $(WARNCFLAGS)
-AM_CXXFLAGS = $(WARNCXXFLAGS)
+AM_CXXFLAGS = $(WARNCXXFLAGS) $(CXX1XCXXFLAGS)
 AM_CPPFLAGS = \
 	-DPKGDATADIR='"$(pkgdatadir)"' \
 	-I$(top_srcdir)/lib/includes \