Fold i386-v4-nat.c into i386-sol2-nat.c

Fold i386-v4-nat.c into i386-sol2-nat.c

I've been carrying around the following patch for some time.  I noticed
that both i386-sol2-nat.c and i386-v4-nat.c are Solaris-only now and it
seems confusing to carry both around.

So this patch merges i386-v4-nat.c into i386-sol2-nat.c, simplifying it
in a couple of places, like removing checks for macros that are always
defined.

Tested on 64-bit Solaris 11.5/x86 (amd64-pc-solaris2.11) and 32-bit
Solaris 11.3/x86 (i386-pc-solaris2.11) half a year ago.

	* i386-v4-nat.c (regmap, supply_gregset, fill_gregset)
	(supply_fpregset, fill_fpregset): Move ...
	* i386-sol2-nat.c [PR_MODEL_NATIVE != PR_MODEL_LP64]: ... here.
	Remove HAVE_GREGSET_T, HAVE_FPREGET_T guards.
	Remove references to ioctl-based procfs.
	Include <sys/reg.h>.
	Remove PR_MODEL_NATIVE guards.
	* configure.nat <sol2, i386> (NATDEPFILES): Remove i386-v4-nat.o.
	* Makefile.in (ALLDEPFILES): Remove i386-v4-nat.c.