loongarch: exclude LARCH_PROLOGUE_TEMP from SIBCALL_REGS [PR 106096]

loongarch: exclude LARCH_PROLOGUE_TEMP from SIBCALL_REGS [PR 106096]

The epilogue may clobber LARCH_PROLOGUE_TEMP ($r13/$t1), so it cannot be
used for sibcalls.

gcc/ChangeLog:

	PR target/106096
	* config/loongarch/loongarch.h (REG_CLASS_CONTENTS): Exclude
	$r13 from SIBCALL_REGS.
	* config/loongarch/loongarch.cc (loongarch_regno_to_class):
	Change $r13 to JIRL_REGS.

gcc/testsuite/ChangeLog:

	PR target/106096
	* g++.target/loongarch/loongarch.exp: New test support file.
	* g++.target/loongarch/pr106096.C: New test.