s390.c (s390_emit_prologue): Do not emit USE insn for GOT register; add REG_MAYBE_DEAD notes instead.

	* config/s390/s390.c (s390_emit_prologue): Do not emit USE
	insn for GOT register; add REG_MAYBE_DEAD notes instead.
	config/s390/s390.md (call, call_value): Add GOT register to
	CALL_INSN_FUNCTION_USAGE where needed.
	(call_exp, call_value_exp): New.

From-SVN: r48908