misc: fix the static vppctl build

Change I58e1ae1c91f4a62e80eaf4e16e9932d8bab17c74 has introduced a reference to config.h,
which is not there in a case of building a static standalone vppctl.

Solution: add a variable STATIC_VPPCTL which, when defined, avoids including
the missing include file. Thanks a lot to Damjan for the suggestion.

Type: fix
Change-Id: I133235ba07e5c2e0d5669be9c2292cab0fdf436f
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>

extras/scripts/build_static_vppctl.sh

@@ -1,4 +1,5 @@
 #/bin/env bash
+set -eu
 
 src=$(realpath $(dirname $0)/../..)/src
 
@@ -8,6 +9,7 @@ ${CC:-cc} \
  -O2 \
  -flto \
  -static \
+ -D STATIC_VPPCTL \
  -I ${src} \
  -g \
  ${src}/vpp/app/vppctl.c \