* rtl.h (LCT_RETURNS_TWICE): New.
* calls.c (emit_call_1): Set current_function_calls_setjmp for
ECF_RETURNS_TWICE.
(emit_library_call_value_1): Map LCT_RETURNS_TWICE
to ECF_RETURNS_TWICE.
* except.c (sjlj_emit_function_enter): Use LCT_RETURNS_TWICE for
call to setjmp.
* unwind-sjlj.c: Invent the setjmp.h declarations if inhibit_libc.