New unit sparc-sol-thread.c extracted from sol-thread.c

New unit sparc-sol-thread.c extracted from sol-thread.c

Moving some sparc-specific routines out of sol-thread.c into their
own (new) file.

gdb/ChangeLog:

        * sol-thread.c (ps_lgetxregsize, ps_lgetxregs, ps_lsetxregs):
        Move these functions to sparc-sol-thread.c.
        * sparc-sol-thread.c: New file.
        * configure.ac: Add sparc-sol-thread.o to CONFIG_OBS and
        sparc-sol-thread.c to CONFIG_SRCS for sparc-solaris native
        configurations.
        * configure: Regenerate.