ada: c++: Get rid of libposix4, librt on Solaris

ada: c++: Get rid of libposix4, librt on Solaris

I recently noticed that neither libposix4 nor librt are needed on
Solaris 11 any longer:

* libposix4 was renamed to librt in Solaris 7 back in 1998.

* librt was folded into libc in the OpenSolaris timeframe, leaving librt
  only as a filter on libc.  Thus, it's no longer needed on either
  Solaris 11 or Illumos.

The following patch removes both uses.  At the same time, Ada's use of
libthread has gone: it was folded into libc in Solaris 10 already.
TIME_LIBRARY and friends in g++ are likewise removed: Solaris was the
only user.

Bootstrapped without regressions on i386-pc-solaris2.11,
sparc-sun-solaris2.11, and x86_64-pc-linux-gnu.

2020-11-16  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/cp:
	* g++spec.c (TIMELIB, TIME_LIBRARY): Remove.
	(lang_specific_driver): Remove TIME_LIBRARY handling.

	gcc:
	* config/sol2.h (TIME_LIBRARY): Remove.

	libstdc++-v3:
	* acinclude.m4 (GLIBCXX_ENABLE_LIBSTDCXX_TIME): Remove libposix4
	references.
	<solaris*>: Don't use -lrt any longer.
	* configure: Regenerate.

	* doc/xml/manual/configure.xml (--enable-libstdcxx-time=OPTION):
	Remove libposix4 reference.

	gcc/ada:
	* Makefile.rtl <sparc*-sun-solaris*> (THREADSLIB): Remove.
	(MISCLIB): Remove -lposix4.
	<*86-*-solaris2*>: Likewise.
	* libgnarl/s-osinte__solaris.ads (System.OS_Interface): Remove
	-lposix4 -lthread.