Remove obsolete OS handling in GN.

tools/gn/variables.cc

 // 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.
 
 #include "tools/gn/variables.h"
 
 namespace variables {
 
 // Built-in variables ----------------------------------------------------------
 
@@ skipping 862 matching lines @@
     "  the library include path. Unlike a normal list of files, they will be\n"
     "  passed to the linker unmodified rather than being treated as file\n"
     "  names relative to the current build file. Generally you would set\n"
     "  the \"lib_dirs\" so your library is found. If you need to specify\n"
     "  a path, you can use \"rebase_path\" to convert a path to be relative\n"
     "  to the build directory.\n"
     "\n"
     "  When constructing the linker command, the \"lib_prefix\" attribute of\n"
     "  the linker tool in the current toolchain will be prepended to each\n"
     "  library. So your BUILD file should not specify the switch prefix\n"
-    "  (like \"-l\"). On Mac, libraries ending in \".framework\" will be\n"
-    "  special-cased: the switch \"-framework\" will be prepended instead of\n"
-    "  the lib_prefix, and the \".framework\" suffix will be trimmed.\n"
+    "  (like \"-l\").\n"
+    "\n"
+    "  Libraries ending in \".framework\" will be special-cased: the switch\n"
+    "  \"-framework\" will be prepended instead of the lib_prefix, and the\n"
+    "  \".framework\" suffix will be trimmed. This is to support the way Mac\n"
+    "  links framework dependencies.\n"
     COMMON_LIB_INHERITANCE_HELP
     COMMON_ORDERING_HELP
     "\n"
     "Examples\n"
     "\n"
     "  On Windows:\n"
     "    libs = [ \"ctl3d.lib\" ]\n"
     "  On Linux:\n"
     "    libs = [ \"ld\" ]\n";
 
@@ skipping 506 matching lines @@
     INSERT_VARIABLE(Sources)
     INSERT_VARIABLE(Testonly)
     INSERT_VARIABLE(Visibility)
   }
   return info_map;
 }
 
 #undef INSERT_VARIABLE
 
 }  // namespace variables