conformtest: clean up POSIX expectations for unistd.h.

conformtest: clean up POSIX expectations for unistd.h.

Concluding the series of patches to clean up conformtest expectations
for "POSIX" (POSIX.1:1995/6, union with POSIX.2:1993), this patch
cleans up expectations for unistd.h.  Tested x86_64; the new XFAIL is
for missing _POSIX2_C_VERSION.

	* conform/data/unistd.h-data (_POSIX_VERSION): Require.
	(_POSIX2_C_VERSION): Require if [POSIX || XPG3 || XPG4 || UNIX98].
	Do not mention otherwise.
	[POSIX] (_XOPEN_VERSION): Do not expect.
	[POSIX] (_XOPEN_XCU_VERSION): Likewise.
	[POSIX] (_POSIX2_C_BIND): Likewise.
	[POSIX] (_POSIX2_VERSION): Likewise.
	[POSIX] (_XOPEN_XPG2): Likewise.
	[POSIX] (_XOPEN_XPG3): Likewise.
	[POSIX] (_XOPEN_XPG4): Likewise.
	[POSIX] (_XOPEN_UNIX): Likewise.
	[POSIX] (_POSIX_ADVISORY_INFO): Likewise.
	[POSIX] (_POSIX_BARRIERS): Likewise.
	[POSIX] (_POSIX_CLOCK_SELECTION): Likewise.
	[POSIX] (_POSIX_CPUTIME): Likewise.
	[POSIX] (_POSIX_MONOTONIC_CLOCK): Likewise.
	[POSIX] (_POSIX_READER_WRITER_LOCKS): Likewise.
	[POSIX] (_POSIX_SHELL): Likewise.
	[POSIX] (_POSIX_SPAWN): Likewise.
	[POSIX] (_POSIX_SPIN_LOCKS): Likewise.
	[POSIX] (_POSIX_SPORADIC_SERVER): Likewise.
	[POSIX] (_POSIX_THREAD_CPUTIME): Likewise.
	[POSIX] (_POSIX_TYPED_MEMORY_OBJECTS): Likewise.
	[POSIX] (_POSIX_THREAD_SPORADIC_SERVER): Likewise.
	[POSIX] (_XBS5_ILP32_OFF32): Likewise.
	[POSIX] (_XBS5_ILP32_OFBIG): Likewise.
	[POSIX] (_XBS5_LP64_OFF64): Likewise.
	[POSIX] (_XBS5_LPBIG_OFFBIG): Likewise.
	[POSIX] (_POSIX_TIMEOUTS): Likewise.
	[POSIX] (_POSIX2_PBS): Likewise.
	[POSIX] (_POSIX2_PBS_ACCOUNTING): Likewise.
	[POSIX] (_POSIX2_PBS_CHECKPOINT): Likewise.
	[POSIX] (_POSIX2_PBS_LOCATE): Likewise.
	[POSIX] (_POSIX2_PBS_MESSAGE): Likewise.
	[POSIX] (_POSIX2_PBS_TRACK): Likewise.
	[POSIX] (_POSIX_TIMESTAMP_RESOLUTION): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFF32_CFLAGS): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFF32_LDFLAGS): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFF32_LIBS): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFF32_LINTFLAGS): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFFBIG_CFLAGS): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFFBIG_LDFLAGS): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFFBIG_LIBS): Likewise.
	[POSIX] (_CS_XBS5_ILP32_OFFBIG_LINTFLAGS): Likewise.
	[POSIX] (_CS_XBS5_LP64_OFF64_CFLAGS): Likewise.
	[POSIX] (_CS_XBS5_LP64_OFF64_LDFLAGS): Likewise.
	[POSIX] (_CS_XBS5_LP64_OFF64_LIBS): Likewise.
	[POSIX] (_CS_XBS5_LP64_OFF64_LINTFLAGS): Likewise.
	[POSIX] (_CS_XBS5_LPBIG_OFFBIG_CFLAGS): Likewise.
	[POSIX] (_CS_XBS5_LPBIG_OFFBIG_LDFLAGS): Likewise.
	[POSIX] (_CS_XBS5_LPBIG_OFFBIG_LIBS): Likewise.
	[POSIX] (_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS): Likewise.
	[POSIX] (_SC_2_C_BIND): Likewise.
	[POSIX] (_SC_2_C_VERSION): Likewise.
	[POSIX] (_SC_2_PBS): Likewise.
	[POSIX] (_SC_2_PBS_ACCOUNTING): Likewise.
	[POSIX] (_SC_2_PBS_CHECKPOINT): Likewise.
	[POSIX] (_SC_2_PBS_LOCATE): Likewise.
	[POSIX] (_SC_2_PBS_MESSAGE): Likewise.
	[POSIX] (_SC_2_PBS_TRACK): Likewise.
	[POSIX] (_SC_ATEXIT_MAX): Likewise.
	[POSIX] (_SC_BARRIERS): Likewise.
	[POSIX] (_SC_BASE): Likewise.
	[POSIX] (_SC_CLOCK_SELECTION): Likewise.
	[POSIX] (_SC_DEVICE_IO): Likewise.
	[POSIX] (_SC_DEVICE_SPECIFIC): Likewise.
	[POSIX] (_SC_DEVICE_SPECIFIC_R): Likewise.
	[POSIX] (_SC_FD_MGMT): Likewise.
	[POSIX] (_SC_FIFO): Likewise.
	[POSIX] (_SC_FILE_ATTRIBUTES): Likewise.
	[POSIX] (_SC_FILE_LOCKING): Likewise.
	[POSIX] (_SC_FILE_SYSTEM): Likewise.
	[POSIX] (_SC_IOV_MAX): Likewise.
	[POSIX] (_SC_MONOTONIC_CLOCK): Likewise.
	[POSIX] (_SC_NETWORKING): Likewise.
	[POSIX] (_SC_PAGE_SIZE): Likewise.
	[POSIX] (_SC_PASS_MAX): Likewise.
	[POSIX] (_SC_PIPE): Likewise.
	[POSIX] (_SC_READER_WRITER_LOCKS): Likewise.
	[POSIX] (_SC_REGEXP): Likewise.
	[POSIX] (_SC_SHELL): Likewise.
	[POSIX] (_SC_SIGNALS): Likewise.
	[POSIX] (_SC_SINGLE_PROCESS): Likewise.
	[POSIX] (_SC_SPIN_LOCKS): Likewise.
	[POSIX] (_SC_TYPED_MEMORY_OBJECTS): Likewise.
	[POSIX] (_SC_USER_GROUPS): Likewise.
	[POSIX] (_SC_USER_GROUPS_R): Likewise.
	[POSIX] (_SC_STREAMS): Likewise.
	[POSIX] (_SC_XBS5_ILP32_OFF32): Likewise.
	[POSIX] (_SC_XBS5_ILP32_OFFBIG): Likewise.
	[POSIX] (_SC_XBS5_LP64_OFF64): Likewise.
	[POSIX] (_SC_XBS5_LPBIG_OFFBIG): Likewise.
	[POSIX] (_SC_THREAD_ROBUST_PRIO_INHERIT): Likewise.
	[POSIX] (_SC_THREAD_ROBUST_PRIO_PROTECT): Likewise.
	[POSIX] (_PC_FILESIZEBITS): Likewise.
	[POSIX] (_PC_REC_INCR_XFER_SIZE): Likewise.
	[POSIX] (_PC_REC_MAX_XFER_SIZE): Likewise.
	[POSIX] (_PC_REC_MIN_XFER_SIZE): Likewise.
	[POSIX] (_PC_REC_XFER_ALIGN): Likewise.
	[POSIX] (uid_t): Likewise.
	[POSIX] (gid_t): Likewise.
	[POSIX] (off_t): Likewise.
	[POSIX] (pid_t): Likewise.
	[POSIX] (cuserid): Allow.
	(_SC_2_CHAR_TERM): Require constant.
	(_POSIX_ASYNCHRONOUS_IO): Remove duplicate optional-constant.
	* conform/Makefile (test-xfail-POSIX/unistd.h/conform): New
	variable.