LoongArch: Implement TARGET_CAN_INLINE_P[PR121875].

LoongArch: Implement TARGET_CAN_INLINE_P[PR121875].

Because LoongArch does not implement TARGET_CAN_INLINE_P,
functions with the target attribute set and those without
it cannot be inlined.  At the same time, setting the
always_inline attribute will cause compilation failure.

To solve this problem, I implemented this hook. During the
implementation process, it checks the status of the target
special options of the caller and callee, such as the ISA
extension.

	PR target/121875

gcc/ChangeLog:

	* config/loongarch/loongarch.cc
	(loongarch_can_inline_p): New function.
	(TARGET_CAN_INLINE_P): Define.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/can_inline_1.c: New test.
	* gcc.target/loongarch/can_inline_2.c: New test.
	* gcc.target/loongarch/can_inline_3.c: New test.
	* gcc.target/loongarch/can_inline_4.c: New test.
	* gcc.target/loongarch/can_inline_5.c: New test.
	* gcc.target/loongarch/can_inline_6.c: New test.
	* gcc.target/loongarch/pr121875.c: New test.