jik:/tmp!88> cat foo.c
typedef struct
{
  int foo;
} foo_t;

#define CONST_FOO (foo_t) { 0 }

foo_t foo[5][5] = { [ 0 ... 4 ] = { [ 0 ... 4 ] = CONST_FOO } };
jik:/tmp!89> gcc -c foo.c
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[0][0]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[0][1]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[0][2]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[0][3]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[0][4]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[0]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[1]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[2]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[3]')
foo.c:8: initializer element is not constant
foo.c:8: (near initialization for `foo[4]')
jik:/tmp!90> 

If you change the #define to "#define CONST_FOO { 0 }", it compiles.  It
compiles *without* that change with gcc 2.95.2.