stdio-common/Makefile: readd bug26 testcase

This testcase was accidentally removed in commit a5357b7c.
Avoid infinite loop in nss_dns getnetbyname [BZ #17630]
Fix warning in elf/tst-unique4lib.cc.
Fix warning in misc/tst-mntent2.c.
Ignore warning in string/tester.c.
Modify stdio-common/tst-fseek.c to use test-skeleton.c

This test needs a TIMEOUT longer than the default 2 seconds since it
sleeps twice for a second each.
Modify stdlib/tst-bsearch.c to use test-skeleton.c

This test used to define a 'struct entry' that conflicts with the
definition in search.h included in test-skeleton. The struct is
now renamed 'item'.
Modify libio/tst-fopenloc.c to use test-skeleton.c

This test would earlier fail when run under test-skeleton.c due to
bug #17522 in 'fputws'. That bug is now fixed and so this test may
be modified.
Fix 'array subscript is above array bounds' warning in res_send.c

I see this warning in my build on F21 x86_64, which seems to be due to
a weak check for array bounds.  Fixed by making the bounds check
stronger.

This is not an actual bug since nscount is never set to anything
greater than MAXNS.  The compiler however does not know this, so we
need the stronger bounds check to quieten the compiler.
Fix the 'array subscript is above array bounds' warning correctly

Use DIAG_IGNORE_NEEDS_COMMENT instead since the compiler should have
seen that NS never goes beyond MAXNS.
Remove some semaphore.h linknamespace XFAILs.

Roland's recent sem_* changes introduced some XPASSes for semaphore.h
linknamespace tests by removing a non-static variable "mountpoint".
This patch removes the XFAILs for the fixed bug.

Tested for x86_64.

	* conform/Makefile (test-xfail-UNIX98/semaphore.h/linknamespace):
	Remove variable.
	(test-xfail-XOPEN2K/semaphore.h/linknamespace): Likewise.
	(test-xfail-XOPEN2K8/semaphore.h/linknamespace): Likewise.
Fix resolver if_* namespace (bug 17717).

Resolver code, brought in by pthreads (at least), uses if_* interfaces
that weren't in POSIX before 2001, resulting in linknamespace
failures.  This patch changes those interfaces to be weak aliases of
__if_* and makes the resolver use __if_* directly.

Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by this patch).

	[BZ #17717]
	* inet/if_index.c (if_nametoindex): Rename to __if_nametoindex and
	define as weak alias of __if_nametoindex.  Use libc_hidden_weak.
	(if_indextoname): Rename to __if_indextoname and define as weak
	alias of __if_indextoname.  Use libc_hidden_weak.
	(if_freenameindex): Rename to __if_freenameindex and define as
	weak alias of __if_freenameindex.
	(if_nameindex): Rename to __if_nameindex and define as weak alias
	of __if_nameindex.
	* sysdeps/mach/hurd/if_index.c (if_nametoindex): Rename to
	__if_nametoindex and define as weak alias of __if_nametoindex.
	Use libc_hidden_weak.
	(if_freenameindex): Rename to __if_freenameindex and define as
	weak alias of __if_freenameindex.
	(if_nameindex): Rename to __if_nameindex and define as weak alias
	of __if_nameindex.
	(if_indextoname): Rename to __if_indextoname and define as weak
	alias of __if_indextoname.  Use libc_hidden_weak.
	* sysdeps/unix/sysv/linux/if_index.c (if_nametoindex): Rename to
	__if_nametoindex and define as weak alias of __if_nametoindex.
	Use libc_hidden_weak.
	(if_freenameindex): Rename to __if_freenameindex and define as
	weak alias of __if_freenameindex.  Use libc_hidden_weak.
	(if_nameindex_netlink): Use __if_freenameindex instead of
	if_freenameindex.
	(if_nameindex): Rename to __if_nameindex and define as weak alias
	of __if_nameindex.  Use libc_hidden_weak.
	(if_indextoname): Rename to __if_indextoname and define as weak
	alias of __if_indextoname.  Use libc_hidden_weak.
	* include/net/if.h [!_ISOMAC] (__if_nametoindex): Declare and use
	libc_hidden_proto.
	[!_ISOMAC] (__if_freenameindex): Likewise.
	* resolv/res_init.c (__res_vinit): Use __if_nametoindex instead of
	if_nametoindex.
	* conform/Makefile (test-xfail-XPG4/grp.h/linknamespace): Remove
	variable.
	(test-xfail-XPG4/pwd.h/linknamespace): Likewise.
	(test-xfail-UNIX98/aio.h/linknamespace): Likewise.
	(test-xfail-UNIX98/grp.h/linknamespace): Likewise.
	(test-xfail-UNIX98/pthread.h/linknamespace): Likewise.
	(test-xfail-UNIX98/pwd.h/linknamespace): Likewise.
	(test-xfail-UNIX98/sched.h/linknamespace): Likewise.
	(test-xfail-UNIX98/time.h/linknamespace): Likewise.
Fix x86_64 memrchr namespace (bug 17719).

On x86_64, memrchr (not a standard function) is defined as a strong
symbol, instead of a weak alias of __memrchr as on other
architectures.  This results in linknamespace test failures from the
use of __memrchr from dirname.  (Not a conformance issue because of
the mem* reservation, but contrary to glibc conventions.)  This patch
makes x86_64 follow other architectures by defining memrchr as a weak
alias.

Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by the patch).

	[BZ #17719]
	* sysdeps/x86_64/memrchr.S (memrchr): Rename to __memrchr and
	define as weak alias of __memrchr.
	(__memrchr): Do not define as strong alias of memrchr.
	* conform/Makefile (test-xfail-XPG4/libgen.h/linknamespace):
	Remove variable.
	(test-xfail-UNIX98/libgen.h/linknamespace): Likewise.
	(test-xfail-XOPEN2K/libgen.h/linknamespace): Likewise.
	(test-xfail-XOPEN2K8/libgen.h/linknamespace): Likewise.
Use pragmas rather than makefiles for necessary options for unwind code.
Revert "Use pragmas rather than makefiles for necessary options for unwind code."

This reverts commit c324fcfe75c3976ae0b16943df00710e1d0d74f7.
Use PTR_MANGLE on libgcc unwinder function pointers.