Fix a problem assembling AArch64 sources when a relocation is generated against a...

Fix a problem assembling AArch64 sources when a relocation is generated against a symbol that has a defined value.

	PR 27217
	* config/tc-aarch64.c (my_get_expression): Rename to
	aarch64_get_expression.  Add a fifth argument to enable deferring
	of expression resolution.
	(parse_typed_reg): Update calls to my_get_expression.
	(parse_vector_reg_list): Likewise.
	(parse_immediate_expression): Likewise.
	(parse_big_immediate): Likewise.
	(parse_shift): Likewise.
	(parse_shifter_operand_imm): Likewise.
	(parse_operands): Likewise.
	(parse_shifter_operand_reloc): Update calls to my_get_expression
	and call aarch64_force_reloc to determine the value of the new
	fifth argument.
	(parse_address_main): Likewise.
	(parse_half): Likewise.
	(parse_adrp): Likewise.
	(aarch64_force_reloc): New function.  Contains code extracted from...
	(aarch64_force_relocation): ... here.
	* testsuite/gas/aarch64/pr27217.s: New test case.
	* testsuite/gas/aarch64/pr27217.d: New test driver.