(mostly) working wtf / wtf_unittests gn targets

tools/gn/secondary/third_party/libxml/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Define an "os_include" variable that points at the OS-specific generated
 # headers.  These were generated by running the configure script offline.
 if (is_linux) {
   os_include = "linux"
 } else if (is_mac) {
   os_include = "mac"
@@ skipping 137 matching lines @@
   deps = [
     "//third_party/icu:icuuc",
     "//third_party/zlib:chrome_zlib",
   ]
 
   if (is_linux) {
     # We need dl for dlopen() and friends.
     ldflags = [ "-ldl" ]
   }
 
+  if (is_mac || is_android) {
+    # http://www.xmlsoft.org/threads.html says that this is required

[Nico, 2013/10/02 15:56:30]

Looking at that page, it seems to no longer say that, "starting with 2.4.7".
third_party/libxml/README.chromium claims we're at 2.7.7.

+    # when using libxml from several threads, which can possibly happen
+    # in chrome. On linux, this is picked up by transitivity from
+    # pkg-config output from build/linux/system.gyp.
+    cflags = [ "-D_REENTRANT" ]
+  }
+
   if (is_clang) {
     cflags = [
       # libxml passes `const unsigned char*` through `const char*`.
       "-Wno-pointer-sign",
 
       # pattern.c and uri.c both have an intentional `for (...);` /
       # `while(...);` loop. I submitted a patch to move the `'` to its own
       # line, but until that's landed suppress the warning:
       "-Wno-empty-body",
 
       # See http://crbug.com/138571#c8
       "-Wno-ignored-attributes",
     ]
   }
 
   includes = [
     "$os_include",
   ]
 }