Ruby

Use the rb_sys_fail_str macro in signal.c

Let signal.c include "internal/error.h" explicitly to ensure that the
identifier rb_sys_fail_str in signal.c refers to the macro defined in
"internal/error.h" instead of the actual function.

That macro reads errno before evaluating its argument. Without this
change, the rb_signo2signm(sig) expression in the "trap" function in
signal.c will overwrite the errno before the actual rb_sys_fail_str
function reads the errno.