Make NSS work in GN build on Windows.

build/config/compiler/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.
 
 import("//build/config/android/config.gni")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 
 # compiler ---------------------------------------------------------------------
@@ skipping 25 matching lines @@
       "/GS",  # Enable buffer security checking.
       "/EHsc",  # Assume C functions can't throw exceptions and don't catch
                 # structured exceptions (only C++ ones).
       "/FS",  # Preserve previous PDB behavior.
     ]
   } else {
     # Common GCC compiler flags setup.
     # --------------------------------
     cflags += [
       "-fno-strict-aliasing",  # See http://crbug.com/32204
-      "-fvisibility=hidden",
     ]
     cflags_cc += [
       "-fno-exceptions",
       "-fno-threadsafe-statics",
+      # Not exporting C++ inline functions can generally be applied anywhere
+      # so we do so here. Normal function visibility is controlled by
+      # //build/config/gcc:symbol_visibility_hidden.
       "-fvisibility-inlines-hidden",
     ]
 
     # Stack protection.
     if (is_mac) {
       cflags += [ "-fstack-protector-all" ]
     } else if (is_linux) {
       cflags += [ "-fstack-protector", "--param=ssp-buffer-size=4" ]
     }
   }
@@ skipping 232 matching lines @@
   }
 
   if (is_win) {
     defines += [
       "__STD_C",
       "__STDC_CONSTANT_MACROS",
       "__STDC_FORMAT_MACROS",
       "_CRT_RAND_S",
       "_CRT_SECURE_NO_DEPRECATE",
       "_SCL_SECURE_NO_DEPRECATE",
-      "_UNICODE",
-      "UNICODE",
     ]
   }
 
   # Stlport setup. Android uses a different (smaller) version of the STL.
   if (is_android) {
     if (is_clang) {
       # Work around incompatibilities between bionic and clang headers.
       defines += [
         "__compiler_offsetof=__builtin_offsetof",
         "nan=__builtin_nan",
@@ skipping 358 matching lines @@
     cflags = [ "-g1" ]
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }