LoongArch: Support split symbol.

LoongArch: Support split symbol.

Add compilation option '-mexplicit-relocs', and if enable '-mexplicit-relocs'
the symbolic address load instruction 'la.*' will be split into two instructions.
This compilation option enabled by default.

gcc/ChangeLog:

	* common/config/loongarch/loongarch-common.cc:
	Enable '-fsection-anchors' when O1 and more advanced optimization.
	* config/loongarch/genopts/loongarch.opt.in: Add new option
	'-mexplicit-relocs', and enable by default.
	* config/loongarch/loongarch-protos.h (loongarch_split_move_insn_p):
	Delete function declaration.
	(loongarch_split_move_insn): Delete function declaration.
	(loongarch_split_symbol_type): Add function declaration.
	* config/loongarch/loongarch.cc (enum loongarch_address_type):
	Add new address type 'ADDRESS_LO_SUM'.
	(loongarch_classify_symbolic_expression): New function definitions.
	Classify the base of symbolic expression X, given that X appears in
	context CONTEXT.
	(loongarch_symbol_insns): Add a judgment condition TARGET_EXPLICIT_RELOCS.
	(loongarch_split_symbol_type): New function definitions.
	Determines whether the symbol load should be split into two instructions.
	(loongarch_valid_lo_sum_p): New function definitions.
	Return true if a LO_SUM can address a value of mode MODE when the LO_SUM
	symbol has type SYMBOL_TYPE.
	(loongarch_classify_address): Add handling of 'LO_SUM'.
	(loongarch_address_insns): Add handling of 'ADDRESS_LO_SUM'.
	(loongarch_signed_immediate_p): Sort code.
	(loongarch_12bit_offset_address_p): Return true if address type is ADDRESS_LO_SUM.
	(loongarch_const_insns): Add handling of 'HIGH'.
	(loongarch_split_move_insn_p): Add the static attribute to the function.
	(loongarch_emit_set): New function definitions.
	(loongarch_call_tls_get_addr): Add symbol handling when defining TARGET_EXPLICIT_RELOCS.
	(loongarch_legitimize_tls_address): Add symbol handling when defining the
	TARGET_EXPLICIT_RELOCS macro.
	(loongarch_split_symbol): New function definitions. Split symbol.
	(loongarch_legitimize_address): Add codes see if the address can split into a high part
	and a LO_SUM.
	(loongarch_legitimize_const_move): Add codes split moves of symbolic constants into
	high and low.
	(loongarch_split_move_insn): Delete function definitions.
	(loongarch_output_move): Add support for HIGH and LO_SUM.
	(loongarch_print_operand_reloc): New function definitions.
	Print symbolic operand OP, which is part of a HIGH or LO_SUM in context CONTEXT.
	(loongarch_memmodel_needs_release_fence): Sort code.
	(loongarch_print_operand): Rearrange alphabetical order and add H and L to support HIGH
	and LOW output.
	(loongarch_print_operand_address): Add handling of 'ADDRESS_LO_SUM'.
	(TARGET_MIN_ANCHOR_OFFSET): Define macro to -IMM_REACH/2.
	(TARGET_MAX_ANCHOR_OFFSET): Define macro to IMM_REACH/2-1.
	* config/loongarch/loongarch.md (movti): Delete the template.
	(*movti): Delete the template.
	(movtf): Delete the template.
	(*movtf): Delete the template.
	(*low<mode>): New template of normal symbol low address.
	(@tls_low<mode>): New template of tls symbol low address.
	(@ld_from_got<mode>): New template load address from got table.
	(@ori_l_lo12<mode>): New template.
	* config/loongarch/loongarch.opt: Update from loongarch.opt.in.
	* config/loongarch/predicates.md: Add support for symbol_type HIGH.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/func-call-1.c: Add build option '-mno-explicit-relocs'.
	* gcc.target/loongarch/func-call-2.c: Add build option '-mno-explicit-relocs'.
	* gcc.target/loongarch/func-call-3.c: Add build option '-mno-explicit-relocs'.
	* gcc.target/loongarch/func-call-4.c: Add build option '-mno-explicit-relocs'.
	* gcc.target/loongarch/func-call-5.c: New test.
	* gcc.target/loongarch/func-call-6.c: New test.
	* gcc.target/loongarch/func-call-7.c: New test.
	* gcc.target/loongarch/func-call-8.c: New test.
	* gcc.target/loongarch/relocs-symbol-noaddend.c: New test.