[AArch64] Make LD testcases support ILP32 mode

[AArch64] Make LD testcases support ILP32 mode

ld/
	* testsuite/ld-aarch64/aarch64-elf.exp (aarch64_choose_lp64_emul): New
	function.
	(run_dump_test_lp64): New function which pass LP64 mode options to both
	assembler and linker when building test binary.
	(aarch64elftests): Remove eh-frame-merge test.
	(eh-frame-merge-lp64): Restrict eh-frame-merge test to LP64 only.
	(run_dump_test): Migrate to run_dump_test_lp64 if the test source was
	written for LP64 only.
	* testsuite/ld-aarch64/erratum843419.d: Support ILP32 mode.
	* testsuite/ld-aarch64/farcall-b-defsym.d: Likewise.
	* testsuite/ld-aarch64/farcall-b-plt.d: Likewise.
	* testsuite/ld-aarch64/farcall-b.d: Likewise.
	* testsuite/ld-aarch64/farcall-bl-defsym.d: Likewise.
	* testsuite/ld-aarch64/farcall-bl-plt.d: Likewise.
	* testsuite/ld-aarch64/farcall-bl.d: Likewise.
	* testsuite/ld-aarch64/ifunc-15.d: Likewise.
	* testsuite/ld-aarch64/ifunc-16.d: Likewise.
	* testsuite/ld-aarch64/ifunc-5a-local.d: Likewise.
	* testsuite/ld-aarch64/ifunc-5a.d: Likewise.
	* testsuite/ld-aarch64/ifunc-5b-local.d: Likewise.
	* testsuite/ld-aarch64/ifunc-5b.d: Likewise.
	* testsuite/ld-aarch64/ifunc-5r-local.d: Likewise.
	* testsuite/ld-aarch64/ifunc-6a.d: Likewise.
	* testsuite/ld-aarch64/ifunc-6b.d: Likewise.
	* testsuite/ld-aarch64/ifunc-7a.d: Likewise.
	* testsuite/ld-aarch64/ifunc-7b.d: Likewise.
	* testsuite/ld-aarch64/ifunc-8.d: Likewise.
	* testsuite/ld-aarch64/limit-b.d: Likewise.
	* testsuite/ld-aarch64/limit-bl.d: Likewise.