title: Make autotools add --std=c11 to CFLAGS
body: <p>There is no <a href="http://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/C-Compiler.html#C-Compiler" rel="nofollow">mention</a> of a <code>AC_PROG_CC_C11</code> analogue to <code>AC_PROG_CC_C99</code>.</p>
  
  <p>How can I get my autotools project to put <code>--std=c11</code> into <code>CFLAGS</code>?</p>