Remove 'clock()' implementation, print warning

FreeBSD implements 'clock' with an accuracy of 128 ticks-per-second for
compatibility reasons, Linux uses 1000000 per-second. Remove 'clock' and
print an error because it is unlikely that this is the resolution
expected by the application.

Fix #3057

repos/libports/lib/mk/libc-gen.inc

@@ -8,6 +8,9 @@ FILTER_OUT_C += \
 	devname.c feature_present.c getpagesizes.c getvfsbyname.c \
 	setproctitle.c sysconf.c sysctlbyname.c
 
+# the following is a wrapper over rusage, which we cannot provide
+FILTER_OUT_C += clock.c
+
 SRC_C = $(filter-out $(FILTER_OUT_C),$(notdir $(wildcard $(LIBC_GEN_DIR)/*.c)))
 
 # 'sysconf.c' includes the local 'stdtime/tzfile.h'

repos/libports/src/lib/libc/time.cc

@@ -6,7 +6,7 @@
  */
 
 /*
- * Copyright (C) 2010-2017 Genode Labs GmbH
+ * Copyright (C) 2010-2018 Genode Labs GmbH
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -18,6 +18,9 @@
 #include "task.h"
 #include "libc_errno.h"
 
+/* Genode includes */
+#include <base/log.h>
+
 namespace Libc { time_t read_rtc(); }
 
 
@@ -91,3 +94,11 @@ int gettimeofday(struct timeval *tv, struct timezone *)
 	tv->tv_usec = ts.tv_nsec / 1000;
 	return 0;
 }
+
+
+extern "C"
+clock_t clock()
+{
+	Genode::error(__func__, " not implemented, use 'clock_gettime' instead");
+	return -1;
+}