Correction of gdb.dwarf2/pr13961.S

Please consider output of objdump for the executable generated from pr13961.S
-------------
Contents of the .debug_info section:
...
 <1><62>: Abbrev Number: 2 (DW_TAG_class_type)
    <63>   DW_AT_name        : foo2
    <68>   DW_AT_byte_size   : 4
    <69>   DW_AT_decl_file   : 1
    <6a>   DW_AT_decl_line   : 1
    <6b>   DW_AT_sibling     : <0x3f> !!! There is no DIE <0x3f>
...
Contents of the .debug_types section:
...
 <1><25>: Abbrev Number: 8 (DW_TAG_class_type) !! Hand-inserted of size=5
    <26>   DW_AT_specification: <0x2a>
 <1><2a>: Abbrev Number: 2 (DW_TAG_class_type)
    <2b>   DW_AT_name        : foo
    <2f>   DW_AT_byte_size   : 4
    <30>   DW_AT_decl_file   : 1
    <31>   DW_AT_decl_line   : 1
    <32>   DW_AT_sibling     : <0x3f> !!! There is no DIE <0x3f>, should be <44>
 <2><36>: Abbrev Number: 3 (DW_TAG_member)
    <37>   DW_AT_name        : bar
    <3b>   DW_AT_decl_file   : 1
    <3c>   DW_AT_decl_line   : 4
    <3d>   DW_AT_type        : <0x3f> !!! There is no DIE <0x3f>
    <41>   DW_AT_data_member_location: 0
    <42>   DW_AT_accessibility: 1       (public)
 <2><43>: Abbrev Number: 0
 <1><44>: Abbrev Number: 4 (DW_TAG_base_type)
    <45>   DW_AT_byte_size   : 4
    <46>   DW_AT_encoding    : 5        (signed)
    <47>   DW_AT_name        : int
...
---------------
The original assembly is generated from a source file and then
modified to insert DIE, with that the subsequent DIE references
should have been updated, which were not.
It is now getting updated to replace hardcoded DIE references with
label-calculated references.

gdb/testsuite/ChangeLog:

2021-02-16  Alok Kumar Sharma  <AlokKumar.Sharma@amd.com>

	* gdb.dwarf2/pr13961.S: Corrected invalide DIE references.