Remove support for Solaris < 10 (PR gdb/22185)

Remove support for Solaris < 10 (PR gdb/22185)

Given that GCC has obsoleted/removed support for Solaris 9 in GCC 4.9/5 in 2013:

    https://gcc.gnu.org/gcc-4.9/changes.html
    https://gcc.gnu.org/ml/gcc-patches/2013-05/msg00728.html

and the last gdb version that can be compiled with gcc 4.9 is 7.12.1 only when
configured with --disable-build-with-cxx, it's time to obsolete/remove support
for Solaris < 10.

This patch does this, simplifying configure.nat along the way (only a single
sol2 configuration with variants for i386 and sparc).

Some configure checks for older Solaris versions can go, too, and the check
for libthread_db.so.1 removed:

* Since Solaris 10, dlopen has moved to libc and libdl.so is just a
  filter on ld.so.1, so no need to check.

* $RDYNAMIC is already handled above (and is a no-op with Solaris ld
  anyway).

Both proc-service.c and sol-thread.c lose support for (Solaris-only)
PROC_SERVICE_IS_OLD.

The attached revised patch has been tested on sparcv9-sun-solaris2.10,
sparcv9-sun-solaris2.11.4, amd64-pc-solaris2.10, amd64-pc-solaris2.11.4,
and x86_64-pc-linux-gnu.

I've also started an i386-pc-solaris2.9 build to check that it really
stops as expected.

	PR gdb/22185
	* configure.host <*-*-solaris2.[01], *-*-solaris2.[2-9]*>: Mark as
	obsolete.
	Use gdb_host sol2 for i[34567]86-*-solaris2*, x86_64-*-solaris2*.
	Remove i386sol2 support.
	* configure.nat <i386sol2>: Remove.
	<sol2-64>: Fold into ...
	<sol2>: ... this.
	Move common settings to default section.
	Add sol-thread.o.
	* configure.tgt <i[34567]86-*-solaris2.1[0-9]*,
	x86_64-*-solaris2.1[0-9]*>: Rename to ...
	<i[34567]86-*-solaris2*, x86_64-*-solaris2*>: ... this.
	<i[34567]86-*-solaris*>: Remove.
	<sparc-*-solaris2.[0-6], sparc-*-solaris2.[0-6].*>: Remove.

	* configure.ac: Remove wctype in libw check.
	(_MSE_INT_H): Don't define on Solaris 7-9.
	<solaris*>: Remove libthread_db.so.1 check.
	* configure: Regenerate.
	* config.in: Regenerate.

	* proc-service.c: Remove PROC_SERVICE_IS_OLD handling.
	(gdb_ps_prochandle_t, gdb_ps_read_buf_t, gdb_ps_write_buf_t)
	(gdb_ps_size_t): Remove.
	Use base types in users.
	* sol-thread.c: Likewise, also for gdb_ps_addr_t.

	* NEWS (Changes since GDB 8.0): Document Solaris 2.0-9 removal.