LoongArch: Add the macro implementation of mcmodel=extreme.

LoongArch: Add the macro implementation of mcmodel=extreme.

gcc/ChangeLog:

	* config/loongarch/loongarch-protos.h (loongarch_symbol_extreme_p):
	Add function declaration.
	* config/loongarch/loongarch.cc (loongarch_symbolic_constant_p):
	For SYMBOL_PCREL64, non-zero addend of "la.local $rd,$rt,sym+addend"
	is not allowed
	(loongarch_load_tls): Added macro support in extreme mode.
	(loongarch_call_tls_get_addr): Likewise.
	(loongarch_legitimize_tls_address): Likewise.
	(loongarch_force_address): Likewise.
	(loongarch_legitimize_move): Likewise.
	(loongarch_output_mi_thunk): Likewise.
	(loongarch_option_override_internal): Remove the code that detects
	explicit relocs status.
	(loongarch_handle_model_attribute): Likewise.
	* config/loongarch/loongarch.md (movdi_symbolic_off64): New template.
	* config/loongarch/predicates.md (symbolic_off64_operand): New predicate.
	(symbolic_off64_or_reg_operand): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/attr-model-5.c: New test.
	* gcc.target/loongarch/func-call-extreme-5.c: New test.
	* gcc.target/loongarch/func-call-extreme-6.c: New test.
	* gcc.target/loongarch/tls-extreme-macro.c: New test.