Enale -fno-fat-lto-objects by default

[Jan Hubicka <hubicka at ucw dot cz>]

Hi,
this patch switches the default for fat-lto-objects as was documented for a while.
-ffat-lto-objects doubles compilation time and often makes users to not notice that
LTO was not used at all (because they forgot to use gcc-ar/gcc-nm plugins).

Sadly I had to add -ffat-lto-objects to bootstrap. This is because I do not know
how to convince our build machinery to use gcc-ar/gcc-nm during the stage2+

ltobootstrapped/regtested ppc64-linux, OK?

Honza

	* config/bootstrap-lto.mk: Use -ffat-lto-objects.
	* common.opt (ffat-lto-objects): Disable by default.
	* doc/invoke.texi (fat-lto-objects): Update documentation.
	* opts.c: Enable fat-lto-objects on lto plugin disable setups.
Index: config/bootstrap-lto.mk
===================================================================
*** config/bootstrap-lto.mk	(revision 204971)
--- config/bootstrap-lto.mk	(working copy)
***************
*** 1,5 ****
  # This option enables LTO for stage2 and stage3.
  
! STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1
! STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1
  STAGEprofile_CFLAGS += -fno-lto
--- 1,7 ----
  # This option enables LTO for stage2 and stage3.
+ # FIXME: Our build system is not yet able to use gcc-ar wrapper, so we need
+ # to go with -ffat-lto-objects. 
  
! STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects
! STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects
  STAGEprofile_CFLAGS += -fno-lto
Index: gcc/common.opt
===================================================================
*** gcc/common.opt	(revision 204971)
--- gcc/common.opt	(working copy)
*************** ffast-math
*** 1156,1162 ****
  Common
  
  ffat-lto-objects
! Common Var(flag_fat_lto_objects) Init(1)
  Output lto objects containing both the intermediate language and binary output.
  
  ffinite-math-only
--- 1156,1162 ----
  Common
  
  ffat-lto-objects
! Common Var(flag_fat_lto_objects)
  Output lto objects containing both the intermediate language and binary output.
  
  ffinite-math-only
Index: gcc/doc/invoke.texi
===================================================================
*** gcc/doc/invoke.texi	(revision 204971)
--- gcc/doc/invoke.texi	(working copy)
*************** need to support linker plugins to allow
*** 8588,8596 ****
  @command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options
  to these tools. With non fat LTO makefiles need to be modified to use them.
  
! The default is @option{-ffat-lto-objects} but this default is intended to
! change in future releases when linker plugin enabled environments become more
! common.
  
  @item -fcompare-elim
  @opindex fcompare-elim
--- 8588,8595 ----
  @command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options
  to these tools. With non fat LTO makefiles need to be modified to use them.
  
! The default is @option{-fno-fat-lto-objects} on targets with linker plugin
! support.
  
  @item -fcompare-elim
  @opindex fcompare-elim
Index: gcc/opts.c
===================================================================
*** gcc/opts.c	(revision 204971)
--- gcc/opts.c	(working copy)
*************** finish_options (struct gcc_options *opts
*** 806,813 ****
        error_at (loc, "LTO support has not been enabled in this configuration");
  #endif
        if (!opts->x_flag_fat_lto_objects && !HAVE_LTO_PLUGIN)
!         error_at (loc, "-fno-fat-lto-objects are supported only with linker plugin.");
! }
    if ((opts->x_flag_lto_partition_balanced != 0) + (opts->x_flag_lto_partition_1to1 != 0)
         + (opts->x_flag_lto_partition_none != 0) >= 1)
      {
--- 806,817 ----
        error_at (loc, "LTO support has not been enabled in this configuration");
  #endif
        if (!opts->x_flag_fat_lto_objects && !HAVE_LTO_PLUGIN)
! 	{
! 	  if (opts_set->x_flag_fat_lto_objects)
!             error_at (loc, "-fno-fat-lto-objects are supported only with linker plugin.");
! 	  opts->x_flag_fat_lto_objects = 1;
! 	}
!     }
    if ((opts->x_flag_lto_partition_balanced != 0) + (opts->x_flag_lto_partition_1to1 != 0)
         + (opts->x_flag_lto_partition_none != 0) >= 1)
      {