Copy xml files to host

Copy xml files to host

When I run test with board file local-remote-host-native.exp, I see
the following warning,

$ make check RUNTESTFLAGS="--host_board=local-remote-host-native
--target_board=local-remote-host-native tdesc-arch.exp
HOST_DIR=/tmp/foo/"

(gdb) set tdesc filename ../../../../git/gdb/testsuite/gdb.xml/trivial.xml^M
warning: Could not open "../../../../git/gdb/testsuite/gdb.xml/trivial.xml"
(gdb) quit^

because "${srcdir}/gdb.xml/trivial.xml" doesn't exist on host.  This
patch is to copy trivial.xml to host and the warning goes away.

(gdb) set tdesc filename /tmp/foo/trivial.xml^M
(gdb) quit^

tdesc-regs.exp has the similar problem that single-reg.xml may not
exist on host at all, and it should be copied to host too.

gdb/testsuite:

2014-10-17  Yao Qi  <yao@codesourcery.com>

	* lib/gdb.exp (gdb_skip_xml_test): Copy trivial.xml to host.
	* gdb.xml/tdesc-regs.exp: Copy single-reg.xml to host.