Replace empty function parameter lists by a void list

In pure C, empty brackets in the function declaration doesn't mean no
parameters, but unspecified parameters. Make clear, we don't
accept any parameters.

Signed-off-by: Stefan Beller <stefanbeller@googlemail.com>
Merge pull request #5 from stefanbeller/libgraprof_no_empty_declarations

Replace empty function parameter lists by a void list