raise: Fix double declaration with modules 'sigprocmask' and 'sigpipe'.

raise: Fix double declaration with modules 'sigprocmask' and 'sigpipe'.

* lib/signal.in.h (GNULIB_defined_signal_blocking): New macro.
(raise): Remove older, duplicated declaration.
(_gl_raise_SIGPIPE): New declaration.
* lib/sigprocmask.c (_gl_raise_SIGPIPE): New function.
(rpl_raise): Remove function.
* lib/raise.c (rpl_raise, raise): Merge into a single function. Handle
a gnulib-defined SIGPIPE here.
* m4/raise.m4 (gl_FUNC_RAISE): Set REPLACE_RAISE also if the module
'sigprocmask' has detected missing signal-blocking and the module
'sigpipe' is enabled.
Reported by Tatsuro MATSUOKA <tmacchant5@yahoo.co.jp>.