Bug 1078383: Update gdbserver to v7.7. r=mwu

This gdbserver binary is built using:

1. Download gdb 7.7 source from GNU web site and extract to $GDB_SOURCE (such as /opt/build/gdb/gdb-7.7/)
2. Under $B2G_REPO (B2G repo dir, such as ~/git/flame-kk/B2G/),
 2.1 source setup.sh
 2.2 cd $GDB_SOURCE/gdb/gdbserver
 2.3 CFLAGS="--sysroot=$B2G_REPO/prebuilts/ndk/8/platforms/android-14/arch-arm" ./configure --host=arm-linux-androideabi
 2.4 make
 2.5 arm-linux-androideabi-strip ./gdbserver