Fix offset computation for append+ mode on switching from read (BZ #16724)

The offset computation in write mode uses the fact that _IO_read_end
is kept in sync with the external file offset.  This however is not
true when O_APPEND is in effect since switching to write mode ought to
send the external file offset to the end of file without making the
necessary adjustment to _IO_read_end.

Hence in append mode, offset computation when writing should only
consider the effect of unflushed writes, i.e. from _IO_write_base to
_IO_write_ptr.

The wiki has a detailed document that describes the rationale for
offsets returned by ftell in various conditions:

https://sourceware.org/glibc/wiki/File%20offsets%20in%20a%20stdio%20stream%20and%20ftell
ARM: Fix handling of concurrent TLS descriptor resolution

The current code for handling concurrent resolution says that the
ABI for _dl_tlsdesc_resolve_hold is the same as that of
_dl_tlsdesc_lazy_resolver. However _dl_tlsdesc_resolve_hold is
called from the trampoline directly rather than the lazy resolver
stub so, for example, r2 has not been pushed so does not needed
to be restored.

This fixes an intermittent failure in nptl/tst-tls3 when building
glibc for arm-linux-gnueabihf with -mtls-dialect=gnu2.

ChangeLog:

2014-05-27  Will Newton  <will.newton@linaro.org>

	[BZ #16990]
	* sysdeps/arm/dl-tlsdesc.S (_dl_tlsdesc_resolve_hold): Save
	and restore r2 rather than just restoring.
Remove second argument from TLS_INIT_TP macro
Remove duplicate code in elf/dl-deps.c.
SH: Convert fork.c to arch-fork.h
IA64: Convert fork.c to arch-fork.h