AC_DECL_SYS_SIGLIST no longer works

[Werner LEMBERG]

[autoconf 2.57]

With autoconf 2.54, a call to AC_DECL_SYS_SIGLIST gives

  checking for sys_siglist declaration in signal.h or unistd.h... yes

With 2.57, I get

  checking whether sys_siglist is declared... no

Reason is that `signal.h' is no longer included; only the default
set of header files is used.


    Werner