Apropos recent debuginfo-related cygwin failures: "Dwarf Error: Could not find,> abbrev number 1"

[Dave Korn <dave dot korn dot cygwin at googlemail dot com>]

... I seem to have had a couple of experiences lately where if there were
undefined references in a .o file, ld complained about mangled dwarf2 info.
On today's CVS head, there is a new testcase FAILure in
"ld-undefined/undefined.exp" that appears to recreate this problem:

> spawn [open ...]
> /gnu/binutils/newsrc/obj/ld/.libs/ld-new: warning: cannot find entry symbol
> start; defaulting to 00401000
> /gnu/binutils/newsrc/obj/ld/.libs/ld-new: Dwarf Error: Could not find
> abbrev number 1.
> tmpdir/undefined.o:undefined.c:(.text+0x5): undefined reference to
> `this_function_is_not_defined'
> /gnu/binutils/newsrc/obj/ld/.libs/ld-new: warning: cannot find entry symbol
> start; defaulting to 00401000
> /gnu/binutils/newsrc/obj/ld/.libs/ld-new: Dwarf Error: Could not find
> abbrev number 1.
> tmpdir/undefined.o:undefined.c:(.text+0x5): undefined reference to
> `this_function_is_not_defined'
> /gnu/binutils/newsrc/obj/ld/.libs/ld-new: warning: cannot find entry symbol
> start; defaulting to 00401000
> /gnu/binutils/newsrc/obj/ld/.libs/ld-new: Dwarf Error: Could not find
> abbrev number 1.
> tmpdir/undefined.o:undefined.c:(.text+0x5): undefined reference to
> `this_function_is_not_defined'
> PASS: undefined
> FAIL: undefined function
> FAIL: undefined line
> testcase /gnu/binutils/newsrc/src/ld/testsuite/ld-undefined/undefined.exp completed in 1 seconds

  I see that this test has not been changed in a long time, so I suspect we
have a real regression here to investigate.  More will follow.

    cheers,
      DaveK