Implement -e trace=%clock option

Implement -e trace=%clock option

linux/*/syscallent.h part is modified automatically by
sed -i 's/0\(,[[:space:]]*SEN(clock_\)/TCL\1/' linux/*/syscallent*.h

[ldv: rewritten clock.test using sched.test as a template]

* sysent.h (TRACE_CLOCK): New macro.
* syscall.c: Alias TCL to TRACE_CLOCK around syscallent.h inclusion.
* qualify.c (lookup_class): Add TRACE_CLOCK for "%clock".
* strace.1 (.SS Filtering): Add information about %clock syscall class.
* NEWS: Mention this change.
* linux/32/syscallent.h: Add TCL flag for clock_* syscalls.
* linux/64/syscallent.h: Likewise.
* linux/alpha/syscallent.h: Likewise.
* linux/arm/syscallent.h: Likewise.
* linux/avr32/syscallent.h: Likewise.
* linux/bfin/syscallent.h: Likewise.
* linux/crisv10/syscallent.h: Likewise.
* linux/hppa/syscallent.h: Likewise.
* linux/i386/syscallent.h: Likewise.
* linux/ia64/syscallent.h: Likewise.
* linux/m68k/syscallent.h: Likewise.
* linux/microblaze/syscallent.h: Likewise.
* linux/mips/syscallent-n32.h: Likewise.
* linux/mips/syscallent-n64.h: Likewise.
* linux/mips/syscallent-o32.h: Likewise.
* linux/powerpc/syscallent.h: Likewise.
* linux/powerpc64/syscallent.h: Likewise.
* linux/s390/syscallent.h: Likewise.
* linux/s390x/syscallent.h: Likewise.
* linux/sh/syscallent.h: Likewise.
* linux/sh64/syscallent.h: Likewise.
* linux/sparc/syscallent.h: Likewise.
* linux/sparc64/syscallent.h: Likewise.
* linux/x32/syscallent.h: Likewise.
* linux/x86_64/syscallent.h: Likewise.
* linux/xtensa/syscallent.h: Likewise.
* tests/clock.test: New test.
* tests/Makefile.am (DECODER_TESTS): Add it.
* tests/ksysent.c (TCL): New macro, defined to 0.
* tests/nsyscalls.c: Likewise.