Portcheck only if --enable-gcc-warnings
Problem reported by Richard Copley (Bug#37852). This patch causes the problem to not occur if one uses plain ‘configure’. The problem can still occur if with ‘configure --enable-gcc-warnings’, so a further fix may be needed. * configure.ac (GNULIB_PORTCHECK, _FORTIFY_SOURCE): Define these only with an explicit --enable-gcc-warnings.