[master] 8a8d6f5ee build: improve wflags.py for gcc

[Nils Goroll]

commit 8a8d6f5ee837593674d8da73e77a0bcd060417dd
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Thu Jun 10 15:49:07 2021 +0200

    build: improve wflags.py for gcc
    
    cc cannot -Wformat-y2k
    
            cc1: warning: -Wformat-y2k ignored without -Wformat [-Wformat-y2k]
    
    cc cannot -Wformat-zero-length
    
            cc1: warning: -Wformat-zero-length ignored without -Wformat [-Wformat-zero-length]

diff --git a/wflags.py b/wflags.py
index 1778fd41b..7cfffea57 100644
--- a/wflags.py
+++ b/wflags.py
@@ -48,8 +48,8 @@ DESIRABLE_WFLAGS = [
     "-Wchar-subscripts",
     "-Wempty-body",
     "-Wextra",
-    "-Wformat-y2k",
-    "-Wformat-zero-length",
+    "-Wformat -Wformat-y2k",
+    "-Wformat -Wformat-zero-length",
     "-Wmissing-field-initializers",
     "-Wmissing-prototypes",
     "-Wnested-externs",
@@ -85,7 +85,7 @@ UNDESIRABLE_WFLAGS = [
 def cc(compiler, opt, obj, src):
     a = [compiler, "-c"]
     if opt is not None:
-        a.append(opt)
+        a += opt.split()
     a += ["-o", obj, src]
 
     try: