package/gdb: disable gdbserver if full gdb is enabled for ARC

package/gdb: disable gdbserver if full gdb is enabled for ARC

With recent update of ARC toolchain to arc-2019.09-eng/rc1 versions
GDB package builds started to fail in autobuilder:

 http://autobuild.buildroot.net/results/bc5/bc52d0012944e15dee30a6e00a92f23c87d0dfda//

This error is caused by 73cc72729a18 ("Move gnulib to top level")
commit in binutils-gdb master branch and appears in ARC case because
arc-2019.09 GDB is based on binutils-gdb master branch and includes
this commit.

More information about this bug can be found there:
https://sourceware.org/bugzilla/show_bug.cgi?id=24729
https://sourceware.org/bugzilla/show_bug.cgi?id=25171
https://github.com/foss-for-synopsys-dwc-arc-processors/binutils-gdb/issues/30

Signed-off-by: Evgeniy Didin <Evgeniy.Didin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: arc-buildroot@synopsys.com
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>