try ignoring bad PLT entries in ELF symbol tables

try ignoring bad PLT entries in ELF symbol tables

Comment says it all:

         /* On ia64-hpux, we have discovered that the system linker
            adds undefined symbols with nonzero addresses that cannot
            be right (their address points inside the code of another
            function in the .text section).  This creates problems
            when trying to determine which symbol corresponds to
            a given address.

            We try to detect those buggy symbols by checking which
            section we think they correspond to.  Normally, PLT symbols
            are stored inside their own section, and the typical name
            for that section is ".plt".  So, if there is a ".plt"
            section, and yet the section name of our symbol does not
            start with ".plt", we ignore that symbol.  */

gdb/ChangeLog:

        * elfread.c (elf_symtab_read): Ignore undefined symbols with
        nonzero addresses if they do not correspond to a .plt section
        when one is available in the objfile.