Fix the build on Windows (#4384)

* Fix errors about Abseil using std::copy

The C++11 version of this function can be unsafe if used improperly.
Defining this macro is also done in the Abseil build, though they don't
export the setting.

* Prevent output differences in generated certificate data

* Don't regenerate nanopb sources on Windows

There's something wrong with the interaction between protoc and the
nanopb generator that prevents this from working properly.

scripts/binary_to_array.py

@@ -152,6 +152,11 @@ def source(namespaces, array_name, array_size_name, fileid, filename,
   Returns:
     A string containing the C/C++ source file.
   """
+
+  if os.name == 'nt':
+    # Force forward slashes on Windows
+    include_name = include_name.replace('\\', '/')
+
   data = []
   data.extend([
       "// Copyright 2019 Google Inc. All Rights Reserved.",