Clean up kernel version conditionals for pre-2.6.32 kernels.

This patch does some initial cleanup, following the move to 2.6.32
minimum kernel version, by removing __LINUX_KERNEL_VERSION
conditionals that are now always-true or always-false.  In the case of
__ASSUME_ARG_MAX_STACK_BASED, where the conditional used a kernel
version that was itself in a macro, the associated sysconf.c code is
also cleaned up and __ASSUME_ARG_MAX_STACK_BASED removed completely.

Tested x86_64 that disassembly of installed shared libraries is
unchanged by the patch.

	* sysdeps/unix/sysv/linux/kernel-features.h [__s390__]
	(__ASSUME_UTIMES): Do not condition on kernel version.
	(__ASSUME_PSELECT): Define unconditionally.
	(__ASSUME_PPOLL): Likewise.
	(__ASSUME_ATFCTS): Likewise.
	(__ASSUME_SET_ROBUST_LIST): Do not condition on kernel version.
	(__ASSUME_COMPLETE_READV_WRITEV): Define unconditionally.
	(__ASSUME_FUTEX_LOCK_PI): Do not condition on kernel version.
	(__ASSUME_UTIMENSAT): Define unconditionally.
	(__ASSUME_PRIVATE_FUTEX): Likewise.
	(__ASSUME_FALLOCATE): Likewise.
	(__ASSUME_O_CLOEXEC): Likewise.
	(__LINUX_ARG_MAX_STACK_BASED_MIN_KERNEL): Remove.
	(__ASSUME_ARG_MAX_STACK_BASED): Likewise.
	(__ASSUME_ADJ_OFFSET_SS_READ): Define unconditionally.
	(__ASSUME_SOCK_CLOEXEC): Do not condition on kernel version.
	(__ASSUME_IN_NONBLOCK): Likewise.
	(__ASSUME_PIPE2): Likewise.
	(__ASSUME_EVENTFD2): Likewise.
	(__ASSUME_SIGNALFD4): Likewise.
	(__ASSUME_DUP3): Likewise.
	[__x86_64__ || __sparc__] (__ASSUME_ACCEPT4_SYSCALL): Likewise.
	(__ASSUME_FUTEX_CLOCK_REALTIME): Define unconditionally.
	(__ASSUME_AT_RANDOM): Likewise.
	(__ASSUME_PREADV): Likewise.
	(__ASSUME_PWRITEV): Likewise.
	(__ASSUME_REQUEUE_PI): Do not condition on kernel version.
	(__ASSUME_F_GETOWN_EX): Define unconditionally.
	(__ASSUME_XFS_RESTRICTED_CHOWN): Likewise.
	* sysdeps/unix/sysv/linux/sysconf.c (__sysconf)
	[!__ASSUME_ARG_MAX_STACK_BASED]: Remove conditional code.
	* sysdeps/unix/sysv/linux/alpha/kernel-features.h
	(__ASSUME_O_CLOEXEC): Define unconditionally.
	(__ASSUME_PSELECT): Do not undefine conditionally.
	(__ASSUME_PPOLL): Likewise.
	(__ASSUME_ATFCTS): Likewise.
	(__ASSUME_SET_ROBUST_LIST): Likewise.
	(__ASSUME_UTIMENSAT): Likewise.
	(__ASSUME_FDATASYNC): Define unconditionally.
	* sysdeps/unix/sysv/linux/arm/kernel-features.h
	(__ASSUME_SIGFRAME_V2): Likewise.
	)__ASSUME_EVENTFD2): Likewise.
	(__ASSUME_SIGNALFD4): Likewise.
	(__ASSUME_PSELECT): Do not undefine conditionally.
	(__ASSUME_PPOLL): Likewise.
	* sysdeps/unix/sysv/linux/ia64/kernel-features.h
	(__ASSUME_PSELECT): Define unconditionally.
	(__ASSUME_PPOLL): Likewise.
	(__ASSUME_O_CLOEXEC): Likewise.
	(__ASSUME_SOCK_CLOEXEC): Likewise.
	(__ASSUME_IN_NONBLOCK): Likewise.
	(__ASSUME_PIPE2): Likewise.
	(__ASSUME_EVENTFD2): Likewise.
	(__ASSUME_SIGNALFD4): Likewise.
	(__ASSUME_DUP3): Likewise.
	* sysdeps/unix/sysv/linux/m68k/kernel-features.h
	(__ASSUME_O_CLOEXEC): Likewise.
	(__ASSUME_SOCK_CLOEXEC): Likewise.
	(__ASSUME_IN_NONBLOCK): Likewise.
	(__ASSUME_PIPE2): Likewise.
	(__ASSUME_EVENTFD2): Likewise.
	(__ASSUME_SIGNALFD4): Likewise.
	(__ASSUME_DUP3): Likewise.
	* sysdeps/unix/sysv/linux/mips/kernel-features.h
	(__ASSUME_EVENTFD2): Likewise.
	(__ASSUME_SIGNALFD4): Likewise.
	(__ASSUME_ACCEPT4_SYSCALL): Likewise.