[master] added redundant 'const' in a function declaration to help SunStudio.

It insists signature match between declarations and definitions even with such
unnecessary qualifiers, and fails to link due to a false-positive
"undefined symbol" at the link time.

src/lib/util/unittests/fork.h

@@ -40,10 +40,10 @@ bool
 process_ok(pid_t process);
 
 pid_t
-provide_input(int *read_pipe, const void *input, const size_t length);
+provide_input(int* read_pipe, const void* input, const size_t length);
 
 pid_t
-check_output(int *write_pipe, const void *output, const size_t length);
+check_output(int* write_pipe, const void* const output, const size_t length);
 
 } // End of the namespace
 }