[debug-early] Disable removal of DW_tags* while generating subprogram DIEs

[Aldy Hernandez <aldyh at redhat dot com>]

This patch disables removing of 
DW_AT_{declaration,object_pointer,formal_parameter} tags while 
generating a DIE for subprograms.  Now that we generate dwarf info 
early, we will always have an old_die the second time around.  I see no 
need to remove the aforementioned tags, only to create them again 
(incorrectly in a C++ testcase I have).

Previously I had the removal predicated by !old_die->dumped_early, hence 
removing it only if it had not been dumped early, but this is 
problematic since types do not have the `dumped_early' flag set.  I 
could add a debug_hook for early_type_decl(), as we did for 
early_global_decl(), so we can tag dumped early types as such, but I'm 
_hoping_ the change here is sufficient.  Things should "just work".  If 
not, perhaps we can look into adding an early_type_decl() hook or some 
other solution.

With this patch I am finally able to build all of libstdc++ without any 
ICEs, all while keeping the guality.exp tests for C at less regressions 
than mainline.

Comitting to branch.  Whine if in violent disagreement.

Aldy

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