configure.ac: Intentionally underquote m4_normalize calls

This works around a bug in Autoconf 2.64 and earlier, which generated
ridiculous symbols like
  /* #undef HAVE_M4_NORMALIZE___FCNTL_H__LANGINFO_H__LIMITS_H__… */
instead of the ones we need.  It was fixed by v2.65~21:
  http://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commitdiff;h=81c80d1bf6c8ddf732d0b89f6fc5e306dac9705e

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

configure.ac

@@ -170,7 +170,7 @@ AC_SEARCH_LIBS([socket], [socket])
 AC_SEARCH_LIBS([inet_addr], [nsl])
 
 # Checks for header files.
-AC_CHECK_HEADERS([m4_normalize([
+AC_CHECK_HEADERS(m4_normalize([
   fcntl.h
   langinfo.h
   limits.h
@@ -191,7 +191,7 @@ AC_CHECK_HEADERS([m4_normalize([
   unistd.h
   wchar.h
   wctype.h
-  ])], [], [AC_MSG_ERROR([Missing required header file.])])
+  ]), [], [AC_MSG_ERROR([Missing required header file.])])
 
 AC_CHECK_HEADERS([pty.h util.h libutil.h paths.h])
 AC_CHECK_HEADERS([endian.h sys/endian.h])
@@ -216,7 +216,7 @@ AC_TYPE_UINTPTR_T
 # Checks for library functions.
 AC_FUNC_FORK
 AC_FUNC_MBRTOWC
-AC_CHECK_FUNCS([m4_normalize([
+AC_CHECK_FUNCS(m4_normalize([
   gettimeofday
   setrlimit
   iswprint
@@ -239,7 +239,7 @@ AC_CHECK_FUNCS([m4_normalize([
   pselect
   getaddrinfo
   getnameinfo
-  ])])
+  ]))
 
 AC_SEARCH_LIBS([clock_gettime], [rt], [AC_DEFINE([HAVE_CLOCK_GETTIME], [1], [Define if clock_gettime is available.])])