gdb/dwarf: skip broken .debug_macro.dwo

Running gdb.base/errno.exp with gcc <= 13 with split DWARF results in:

    $ make check TESTS="gdb.base/errno.exp" RUNTESTFLAGS="CC_FOR_TARGET=gcc-13 --target_board=fission"
    (gdb) break -qualified main
    /home/smarchi/src/binutils-gdb/gdb/dwarf2/read.c:7549: internal-error: locate_dwo_sections: Assertion `!dw_sect->readin' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    ...
    FAIL: gdb.base/errno.exp: macros: gdb_breakpoint: set breakpoint at main (GDB internal error)

The assert being hit has been added in 28f15782adab ("gdb/dwarf: read
multiple .debug_info.dwo sections"), but it merely exposed an existing
problem.

gcc versions <= 13 are affected by this bug:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111409

Basically, it produces .dwo files with multiple .debug_macro.dwo
sections, with some unresolved links between them.  I think that this
macro debug info is unusable, and all we can do is ignore it.

In locate_dwo_sections, if we detect a second .debug_macro.dwo section,
forget about the previous .debug_macro.dwo and any subsequent one.  This
will effectively make it as if the macro debug info wasn't there at all.

The errno test seems happy with it:

    # of expected passes            84
    # of expected failures          8

Change-Id: I6489b4713954669bf69f6e91865063ddcd1ac2c8
Approved-By: Tom Tromey <tom@tromey.com>

0 files changed, 0 insertions, 0 deletions