LoongArch: Add relaxation support for call36 that jump to PLT entry

LoongArch: Add relaxation support for call36 that jump to PLT entry

Part of commit a104f0a3e620 ("LoongArch: Add more relaxation support for
call36") in master.  This part is needed for 2.43 branch to fix a link
failure of QtWebEngine-6.8.1, which can be demonstrated with a reduced
test case (with -shared):

    .text
    .zero 1 << 27   # pretending we have a lot of code in .text
    .globl f        # preemptible, thus must be called via PLT
    f:
      move $a0, $r0
      ret
    g:
      pcaddu18i $t0, %call36(f)
      jr $t0

Signed-off-by: Xi Ruoyao <xry111@xry111.site>