[PATCH] Fix thread-safety follow-out for cross builds (PR libfortran/24991)

[Jakub Jelinek]

On Wed, Nov 23, 2005 at 06:11:21PM +0100, Fran?ois-Xavier Coudert wrote:
> By the way, Jakub, you didn't specify on which platforms you did test
> it (be them native or cross).

I tested on x86_64-linux native, the reporter tested on powerpc*-darwin*
in-tree build (he probably wasn't using cross, just the (unsupported?)
srcdir == objdir configuration) and although he ran into other issues later
on (possibly because of old files in the in-tree build, that's yet to be
seen), this patch made clear progress there (as in, gthr-default.h
has certainly be found while previously it couldn't).

The patch is just a port of what libobjc seems to be doing.
libobjc/Makefile.in has:
INCLUDES = -I$(srcdir)/objc  -I$(srcdir)/$(MULTISRCTOP)../gcc \
  -I$(srcdir)/$(MULTISRCTOP)../gcc/config \
  -I$(MULTIBUILDTOP)../../$(host_subdir)/gcc \
  -I$(srcdir)/$(MULTISRCTOP)../include
and uses the same autoconf hackery to set host_subdir variable
that I introduced in the patch.

	Jakub