Consolidate non cancellable nanosleep call

This patch consolidates all the non cancellable nanosleep calls to use
the __nanosleep_nocancel identifier.  For non cancellable targets it will
be just a macro to call the default respective symbol while on Linux
will be a internal one.

Checked on x86_64-linux-gnu, x86_64-linux-gnu-x32, and i686-linux-gnu.

	* nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock): Replace
	nanosleep_not_cancel with __nanosleep_nocancel.
	* sysdeps/generic/not-cancel.h (nanosleep_not_cancel): Remove macro.
	(__nanosleep_nocancel): New macro.
	* sysdeps/unix/sysv/linux/nanosleep.c (__nanosleep_nocancel): New
	function.
	* sysdeps/unix/sysv/linux/not-cancel.h (nanosleep_not_cancel): Remove
	macro.
	(__nanosleep_nocancel): New prototype.