[build] Move gthr to toplevel libgcc

[John David Anglin]

On 8-Aug-11, at 9:47 AM, Rainer Orth wrote:

> ** _DCE_THREADS is used to select gthr-dce.h, but again dce is the
>   only/default model on hppa[12]*-*-hpux10* (pa-hpux10.h), so the
>   special-casing can be removed.

DCE threads and thread single are both supported.  There are multilibs
for both.  Different libraries are needed for threaded and non  
threaded programs,
and there is no mechanism to detect whether threads are active or not.

>
> I haven't moved two macros used in gthr*.h yet: GTHREAD_USE_WEAK and
> SUPPORTS_WEAK.  This seems to warrant a separate followup patch, but  
> for
> the record I report my findings:
>
> * GTHREAD_USE_WEAK must be defined explicitly.  It needs to be  
> poisoned
>  in system.h after the move.  Right now, only a few targets defined a
>  non-default value:
>
>  darwin.h		#define GTHREAD_USE_WEAK 0
>  i386/cygwin.h		#define GTHREAD_USE_WEAK 0
>
>  ia64/hpux.h		#define GTHREAD_USE_WEAK 0
>  pa/pa64-hpux.h	#define GTHREAD_USE_WEAK 0
>  pa/som.h		#define GTHREAD_USE_WEAK 0
>
>  The last 3 could be handled in a new hpux-lib.h, but perhaps this
>  isn't necessary if ax_sys_weak_alias.m4 works.

I'm not sure this is possible in general on HP-UX.

> * SUPPORTS_WEAK is probably best detected with autoconf.  We have
>  libgfortran/acinclude.m4 (LIBGFOR_GTHREAD_WEAK), but should probably
>  go for m4/ax_sys_weak_alias.m4 from the autoconf-archive instead.  If
>  we're lucky, that macro can detect support for weak definitions and
>  replace both SUPPORTS_WEAK and GTHREAD_USE_WEAK.

There are multiple meanings for SUPPORTS_WEAK.  Within the compiler,
SUPPORTS_WEAK implies that multiple definitions of code and data symbols
are possible.  At the moment, there is no need for undefined weak or  
weak
aliases.  The situation is different in the gthr* headers and compiled  
code
such as libgfortran.

On PA HP-UX, the compiler "weak" support is implemented using COMDAT
and secondary definitions.  Neither of these support undefined weak.

Dave