Fix build failure with GCC 5
Fix build failure with GCC 5

The error is:
clitest.c: In function ‘cmd_test’:
clitest.c:75:45: error: ISO C does not support '__FUNCTION__' predefined identifier [-Werror=pedantic]
     cli_print(cli, "called %s with \"%s\"", __FUNCTION__, command);
                                             ^
Fixed by using __func__ from C99.

dparrish/libcli