Use libc_ifunc macro for clock_* symbols in librt.

Use libc_ifunc macro for clock_* symbols in librt.

This patch uses the libc_ifunc macro to create already existing ifunc functions
clock_getres, clock_gettime, clock_settime, clock_getcpuclockid and
clock_nanosleep. If HAVE_IFUNC is defined, the macro COMPAT_REDIRECT uses
the libc_ifunc macro.
Furthermore some whitespace damage is cleaned.

ChangeLog:

	* rt/clock-compat.c (COMPAT_REDIRECT): Use libc_ifunc macro.