scripts/localplt.awk: Handle DT_JMPREL with empty PLT (for C-SKY)

scripts/localplt.awk: Handle DT_JMPREL with empty PLT (for C-SKY)

On csky-linux-gnuabiv2, binutils 2.33 produces a DT_JMPREL entry
for the dynamic loader if it does not contain any PLT relocations:

Dynamic section at offset 0x1df48 contains 19 entries:
  Tag        Type                         Name/Value
 0x0000000e (SONAME)                     Library soname: [ld-linux-cskyv2-hf.so.1]
 0x00000004 (HASH)                       0xd4
 0x6ffffef5 (GNU_HASH)                   0x1a8
 0x00000005 (STRTAB)                     0x4ac
 0x00000006 (SYMTAB)                     0x28c
 0x0000000a (STRSZ)                      527 (bytes)
 0x0000000b (SYMENT)                     16 (bytes)
 0x00000003 (PLTGOT)                     0x1f000
 0x00000002 (PLTRELSZ)                   0 (bytes)
 0x00000014 (PLTREL)                     RELA
 0x00000017 (JMPREL)                     0xaa4
 0x00000007 (RELA)                       0x75c
 0x00000008 (RELASZ)                     840 (bytes)
 0x00000009 (RELAENT)                    12 (bytes)
 0x6ffffffc (VERDEF)                     0x700
 0x6ffffffd (VERDEFNUM)                  3
 0x6ffffff0 (VERSYM)                     0x6bc
 0x6ffffff9 (RELACOUNT)                  68
 0x00000000 (NULL)                       0x0

This confuses the script:

Unexpected output from check-localplt: …/elf/ld.so.jmprel:
*** DT_JMPREL does not match any section's address

This commit changes the script to record the DT_PLTRELSZ value and
reject DT_JMPREL values not a section boundary only if DT_PLTRELSZ
is present with a non-zero value.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>