x86: Fix DT_JMPREL/DT_PLTRELSZ when relocs share a section

x86: Fix DT_JMPREL/DT_PLTRELSZ when relocs share a section

If a linker script does not place the PLT relocations and "normal"
relocations in separate ELF sections, `ld` will currently output incorrect
values for DT_JMPREL and DT_PLTRELSZ - they cover the entire ELF section,
rather than just the PLT relocations

Don't ignore the extent of the BFD section - use the size of the srelplt
BFD section and its offset from the output_secttion

bfd/

	PR ld/30787
	* elfxx-x86.c (_bfd_x86_elf_finish_dynamic_sections): Use input
	section for DT_JMPREL and DT_PLTRELSZ.

ld/

	PR ld/30787
	* testsuite/ld-i386/i386.exp: Run pr30787.
	* testsuite/ld-x86-64/x86-64.exp: Likewise.
	* testsuite/ld-i386/pr30787.d: New file.
	* testsuite/ld-i386/pr30787.s: Likewise.
	* testsuite/ld-i386/pr30787.t: Likewise.
	* testsuite/ld-x86-64/pr30787.d: Likewise.
	* testsuite/ld-x86-64/pr30787.s: Likewise.
	* testsuite/ld-x86-64/pr30787.t: Likewise.