package/gdb: fix gdbserver build with m68k and uclibc

Allow to build gdbserver with m68k and uclibc. This patch is not needed
for version above 9.2 because build_gdbserver as been
moved to its own file since
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=919adfe8409211c726c1d05b47ca59890ee648f1

This new file (gdbserver/configure.srv) does not seem to be affected by
this issue

Fixes:
 - http://autobuild.buildroot.org/results/f4d6d9d8418c0da48a3db4ad5a82e19bd16eae34



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>