LoongArch: Fix eh_return epilogue for normal returns.

LoongArch: Fix eh_return epilogue for normal returns.

On LoongArch, the regitsters $r4 - $r7 (EH_RETURN_DATA_REGNO) will be saved
and restored in the function prologue and epilogue if the given function calls
__builtin_eh_return.  This causes the return value to be overwritten on normal
return paths and breaks a rare case of libgcc's _Unwind_RaiseException.

gcc/ChangeLog:

	PR target/114848
	* config/loongarch/loongarch.cc: Do not restore the saved eh_return
	data registers ($r4-$r7) for a normal return of a function that calls
	__builtin_eh_return elsewhere.
	* config/loongarch/loongarch-protos.h: Same.
	* config/loongarch/loongarch.md: Same.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/eh_return-normal-return.c: New test.

(cherry picked from commit 4b421728289e6f1caa0dfaa953a11698ab95d37d)