BUILD: Also set std compiler flag in boost.m4

Author: DrMcCoy

configure.ac

@@ -167,7 +167,10 @@ if test "x$with_std" = "xyes"; then
 	esac;
 fi
 
+BOOST_STD="$STD"
+
 AC_SUBST(STD)
+AC_SUBST(BOOST_STD)
 
 dnl Link-time optimization
 AC_ARG_WITH([lto], [AS_HELP_STRING([--with-lto], [Compile with link-time optimization @<:@default=no@:>@])], [], [with_lto=no])

m4/boost.m4

@@ -216,9 +216,11 @@ AC_LANG_POP([C++])dnl
         BOOST_CPPFLAGS=
         ;;#(
       *)
-        AC_SUBST([BOOST_CPPFLAGS], ["-I$boost_cv_inc_path"])dnl
+        BOOST_CPPFLAGS="-I$boost_cv_inc_path"
         ;;
     esac
+  BOOST_CPPFLAGS="$BOOST_STD $BOOST_CPPFLAGS"
+  AC_SUBST([BOOST_CPPFLAGS])
   if test x"$boost_cv_inc_path" != xno; then
   AC_DEFINE([HAVE_BOOST], [1],
             [Defined if the requested minimum BOOST version is satisfied])