conformtest: Correct some sys/stat.h expectations for XPG3.

This patch fixes various conformtest sys/stat.h expectations that were
incorrect for XPG3 (not based on a full review, so not necessarily an
exhaustive set of such corrections).  Most of these corrections fix
spurious failures shown in testing (but that for fchmod introduces a
correct failure, as that function is wrongly declared for XPG3, so
this doesn't eliminate any XFAILs).

Tested for x86_64 and x86.

	* conform/data/sys/stat.h-data [XPG3] (S_IFLNK): Do not expect.
	[XPG3] (S_IFSOCK): Likewise.
	[XPG3] (S_ISVTX): Likewise.
	[XPG3] (S_ISLNK): Likewise.
	[XPG3] (S_ISSOCK): Likewise.
	[XPG3] (fchmod): Likewise.
	[XPG3] (lstat): Likewise.
	[XPG3] (mknod): Likewise.