v.in.dxf: fix compilation error

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@55644 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.in.dxf/dxf_to_vect.c

@@ -9,6 +9,7 @@
 #endif
 
 static void make_head(struct Map_info *);
+static int find_next_header_variable(struct dxf_file *);
 
 static struct bound_box ext, dxf_ext;