x86_64: Unconditionally run test elf/check-dt-x86-64-plt

x86_64: Unconditionally run test elf/check-dt-x86-64-plt

The intention of GLIBC_ABI_DT_X86_64_PLT is simply to mark the existence
of the fix in f8587a61892cbafd98ce599131bf4f103466f084
("x86-64: Ignore r_addend for R_X86_64_GLOB_DAT/R_X86_64_JUMP_SLOT").

Testing for GLIBC_ABI_DT_X86_64_PLT does not depend on the linker
supporting -z mark-plt.  Therefore remove this dependency on linker
support and test unconditionally.

Fixes commit 399384e0c8193e31aea014220ccfa24300ae5938
("x86-64: Add GLIBC_ABI_DT_X86_64_PLT [BZ #33212]")

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>