libiberty: lto: Addition of .symtab in elf file.

libiberty: lto: Addition of .symtab in elf file.

    This patch is continutaion of previous patch (bypass-asm: Bypass assembler when
    generating LTO object files.).
    Now the emitted object file contains .symtab along with __gnu_lto_slim symbol.

gcc/ChangeLog:

        * lto-object.cc (lto_obj_file_close):

include/ChangeLog:

        * simple-object.h (simple_object_write_add_symbol):

libiberty/ChangeLog:

        * simple-object-common.h (struct simple_object_symbol_struct):
        * simple-object-elf.c (simple_object_elf_write_ehdr):
        (simple_object_elf_write_symbol):
        (simple_object_elf_write_to_file):
        * simple-object.c (simple_object_start_write):
        (simple_object_write_add_symbol):
        (simple_object_release_write):

Signed-off-by: Rishi Raj <rishiraj45035@gmail.com>