signal-h: Rename from signal.

signal-h: Rename from signal.

* modules/signal-h: Renamed from modules/signal.
* modules/pthread_sigmask (Depends-on): Update.
* modules/raise (Depends-on): Likewise.
* modules/sigaction (Depends-on): Likewise.
* modules/sigpipe (Depends-on): Likewise.
* modules/sigprocmask (Depends-on): Likewise.
* modules/sys_select (Depends-on): Likewise.
* modules/signal-h-tests: Renamed from modules/signal-tests.
(Files, Depends-on, Makefile.am): Update.
* tests/test-signal-h.c: Renamed from tests/test-signal.c.
* modules/signal-h-c++-tests: Renamed from modules/signal-c++-tests.
(Files, Makefile.am): Update.
* tests/test-signal-h-c++.cc: Renamed from tests/test-signal-c++.cc.
* tests/test-signal-h-c++2.cc: Renamed from tests/test-signal-c++2.cc.
* modules/signal: New placeholder file.
* MODULES.html.sh (Support for systems lacking POSIX:2008): Update.
* doc/posix-headers/signal.texi: Update.
* NEWS: Mention the change.