[autotools] Fixes quoting in test for DUNE symbols

Some modules do test for complicated symbols,
eg. "&StandardMerge<double,1,1,1>::build;", which lead to broken
configure scripts. In the above case :
" 1>build;
  ;"
as a shell command.
This patch quotes the program body used for AC_LANG_PROGRAM correctly
to prevent this.

m4/dune.m4

@@ -438,8 +438,8 @@ AC_DEFUN([DUNE_CHECK_MODULES],[
 
           AC_LINK_IFELSE(
             [AC_LANG_PROGRAM(
-              [#]include<dune/[]_dune_header>,
-              _dune_symbol)],
+              [[#]include<dune/[]_dune_header>],
+              [[_dune_symbol]])],
             [dune_cv_lib[]_dune_lib=yes],
             [dune_cv_lib[]_dune_lib=no])
         ])