GN: get echo-headers sources via exec_script

gyp/nanomsg.gyp

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'variables': {
     'skia_warnings_as_errors': 0,
   },
   'targets': [{
     # Draws pictures cross-process.
     'target_name': 'nanomsg_picture_demo',
     'type': 'executable',
     'dependencies': [
       'skia_lib.gyp:skia_lib',
       'flags.gyp:flags',
       'libnanomsg',
     ],
     'sources': [ '../experimental/nanomsg/picture_demo.cpp' ],
   },{
     'target_name': 'libnanomsg',
     'type': 'static_library',
 
     # Clients can include nanomsg public header foo.h with #include "nanomsg/src/foo.h"
     'direct_dependent_settings': {
       'include_dirs': [ '../third_party/externals' ]
     },
 
     'sources': [
-      '<!@(python find.py ../third_party/externals/nanomsg/src "*.c")'
+      '<!@(python find.py "*.c" ../third_party/externals/nanomsg/src)'
     ],
 
     # TODO(mtklein): Support Windows?
     # To refresh: cd third_party/externals/nanomsg; ./autogen.sh; ./configure; copy from Makefile.
     'conditions': [
       ['skia_os == "linux"', {
         'cflags': [ '-w' ],
         'libraries': [
             '-lpthread',
             '-lanl',  # Provides getaddrinfo_a and co.
@@ skipping 80 matching lines @@
           'NN_USE_IFADDRS',
           'NN_USE_KQUEUE',
           'NN_USE_PIPE',
           'STDC_HEADERS',
           '_THREAD_SAFE',
         ],
       }],
     ]
   }]
 }