build: doc: Obsolete Solaris 11.3 support

build: doc: Obsolete Solaris 11.3 support

This patch implements the Solaris 11.[0-3] obsoletion just announced in

	https://gcc.gnu.org/pipermail/gcc/2022-December/240322.html

Bootstrapped without regressions on Solaris 11.3 (i386-pc-solaris2.11,
sparc-sun-solaris2.11 without and with --enable-obsolete) and 11.4.

2022-12-09  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc:
	* config.gcc: Determine Solaris minor version.
	Obsolete *-*-solaris2.11.[0-3]*.
	* doc/install.texi (Specific, *-*-solaris2*): Document it.