Set the default gdb osabi to GNU/Linux.

Bug: http://b/27926981
Change-Id: I9d8da00f74272e4cdcb9bb55d4b0c87411c87d02
diff --git a/gdb-7.11/gdb/configure b/gdb-7.11/gdb/configure
index b523deb..091ec6c 100755
--- a/gdb-7.11/gdb/configure
+++ b/gdb-7.11/gdb/configure
@@ -5813,7 +5813,7 @@
 
 # For other settings, only the main target counts.
 gdb_sim=
-gdb_osabi=
+gdb_osabi=GDB_OSABI_LINUX
 build_gdbserver=
 targ=$target; . ${srcdir}/configure.tgt