dabba: move around 'const' declaration specifier.

cli output is worth 1000 words:

$ cdecl explain "int *a"
declare a as pointer to int
$ cdecl explain "const int *a"
declare a as pointer to const int
$ cdecl explain "const int const *a"
syntax error
$ cdecl explain "const int * const a"
declare a as const pointer to const int

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>