gdb: fix build with gcc 4.1.2 as host compiler

gdb: fix build with gcc 4.1.2 as host compiler

The additional warnings are causing compile errors on gcc version 4.1.2
as a host compiler.

cc -c  -Wall -Wdeclaration-after-statement -Wpointer-arith
-Wpointer-sign -Wno-unused -Wunused-value -Wunused-function -Wno-switch
-Wno-char-subscripts -Wmissing-prototypes -Wdeclaration-after-statement
-Wempty-body -Wmissing-parameter-type -Wold-style-declaration -Wold-
style-definition -Wformat-nonliteral  -I. -I. -I./../../include
filter_host.c
cc1: error: unrecognized command line option "-Wempty-body"
cc1: error: unrecognized command line option "-Wmissing-parameter-type"
cc1: error: unrecognized command line option "-Wold-style-declaration"
cc1: error: unrecognized command line option "-Wempty-body"
cc1: error: unrecognized command line option "-Wmissing-parameter-type"
cc1: error: unrecognized command line option "-Wold-style-declaration"

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>