Fix GDBserver build failure when $development is false

Fix GDBserver build failure when $development is false

When we set bfd/development.sh:$development to false, GDBserver failed to
build,

selftest.o: In function `selftests::run_tests(char const*)':
binutils-gdb/gdb/gdbserver/../common/selftest.c:97:undefined reference to `selftests::reset()'
collect2: error: ld returned 1 exit status

selftest.o shouldn't be compiled and linked when $development is false.
With this patch, in release mode, GDBserver doesn't nothing with option
--selftest,

$ ./gdbserver --selftest=foo
Selftests are not available in a non-development build.
$ ./gdbserver --selftest
Selftests are not available in a non-development build.

gdb/gdbserver:

2018-01-08  Yao Qi  <yao.qi@linaro.org>
	    Simon Marchi  <simon.marchi@ericsson.com>

	* Makefile.in (OBS): Remove selftest.o.
	* configure.ac: Set srv_selftest_objs if $development is true.
	(GDBSERVER_DEPFILES): Append $srv_selftest_objs.
	* configure: Re-generated.
	* server.c (captured_main): Wrap variable selftest_filter with
	GDB_SELF_TEST.

gdb/testsuite:

2018-01-08  Simon Marchi  <simon.marchi@ericsson.com>

	* gdb.server/unittest.exp: Match the output in non-development
	mode.