Support gdb wrappers

Use gdbwrapper() for launching gdb.  This can be redefined to launch
one of the many gdb wrappers instead.

Example:
function gdbwrapper()
{
    ddd --debugger $ANDROID_TOOLCHAIN/$GDB -x "$@"
}

Change-Id: I3cce8a2ca1bae6d531e2388a93cb52075b21a42c

envsetup.sh

@@ -740,6 +740,11 @@ function systemstack()
     adb shell echo '""' '>>' /data/anr/traces.txt && adb shell chmod 776 /data/anr/traces.txt && adb shell kill -3 $(pid system_server)
 }
 
+function gdbwrapper()
+{
+    $ANDROID_TOOLCHAIN/$GDB -x "$@"
+}
+
 function gdbclient()
 {
    local OUT_ROOT=$(get_abs_build_var PRODUCT_OUT)
@@ -796,7 +801,7 @@ function gdbclient()
        echo >>"$OUT_ROOT/gdbclient.cmds" "target remote $PORT"
        echo >>"$OUT_ROOT/gdbclient.cmds" ""
 
-       $ANDROID_TOOLCHAIN/$GDB -x "$OUT_ROOT/gdbclient.cmds" "$OUT_EXE_SYMBOLS/$EXE"
+       gdbwrapper "$OUT_ROOT/gdbclient.cmds" "$OUT_EXE_SYMBOLS/$EXE"
   else
        echo "Unable to determine build system output dir."
    fi