$ cat const.c
#define B0 (+1.0l/5/1/6)

const double c0 = B0; // initializer element is not computable at load time
const double c0_tab[1] = { B0 }; // initializer element is not constant

#define B1 (+1.0l/5)

const double c1 = B1; // ok.
const double c1_tab[1] = { B1 }; // initializer element is not constant

$ gcc const.c
const.c:3: error: initializer element is not computable at load time
const.c:4: error: initializer element is not constant
const.c:4: error: (near initialization for 'c0_tab[0]')
const.c:9: error: initializer element is not constant
const.c:9: error: (near initialization for 'c1_tab[0]')

gcc-4.1.0-rc1 with long-double-128 patchset.