Start using flexible array members

Flexible array members are a C99 feature that avoids "cheating" in the
declaration of variable-length arrays at the end of structs.  With
Autoconf support, this should be transparent for older compilers.

We start with one use in gist.h because gcc 4.6 started to raise a
warning there.  Over time, it can be expanded to other places in the
source, but they will likely need some review of sizeof and offsetof
usage.  The current change in gist.h appears to be safe in this
regard.

1 files changed, 71 insertions, 0 deletions

diff --git a/configure b/configure
index a2c3aab407b..9b8cb48931d 100755
--- a/configure
+++ b/configure
@@ -14954,6 +14954,77 @@ _ACEOF
 
 fi
 
+
+  { $as_echo "$as_me:$LINENO: checking for flexible array members" >&5
+$as_echo_n "checking for flexible array members... " >&6; }
+if test "${ac_cv_c_flexmember+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <stdlib.h>
+	    #include <stdio.h>
+	    #include <stddef.h>
+	    struct s { int n; double d[]; };
+int
+main ()
+{
+int m = getchar ();
+	    struct s *p = malloc (offsetof (struct s, d)
+				  + m * sizeof (double));
+	    p->d[0] = 0.0;
+	    return p->d != (double *) NULL;
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  ac_cv_c_flexmember=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	ac_cv_c_flexmember=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:$LINENO: result: $ac_cv_c_flexmember" >&5
+$as_echo "$ac_cv_c_flexmember" >&6; }
+  if test $ac_cv_c_flexmember = yes; then
+
+cat >>confdefs.h <<\_ACEOF
+#define FLEXIBLE_ARRAY_MEMBER /**/
+_ACEOF
+
+  else
+    cat >>confdefs.h <<\_ACEOF
+#define FLEXIBLE_ARRAY_MEMBER 1
+_ACEOF
+
+  fi
+
 { $as_echo "$as_me:$LINENO: checking for signed types" >&5
 $as_echo_n "checking for signed types... " >&6; }
 if test "${pgac_cv_c_signed+set}" = set; then