c99 lets us do neat stuff like:
{
int j, k;
foo(&j, &k);
int z = j + k;
}
and also
struct point { int x; int y; };
struct point pt = { .x=5, .y=5 };
This commit makes the configure scripts check to make sure your
compiler implements them. It also disables our longstanding warning
about midblock declarations.
Closes ticket 13233.
