-) using dupenv_s instead of getenv_s and calling strdup ourselves.
-) few impossible-to-obtain if checks.
-) various signed/unsigned casting.
-) using time_t instead of time32_t
-) checking output of FormatMessage for failures.
-) don't redefine _WIN32_WINNT without undefining it first.
-) fixed msvc's interlocked casting.
-) renamed AddPort to AddListeningPort.
-) added protobuf's third_party includes to search path.
-) added a missing definition for inet_ntop in mingw32.
-) removed useless declarations.

First: ugh.

Second: allow tracer global variables to be registered and then parsed out of a configuration environment variable.

Expose TSI trace config variable directly to ease this a little.

- Renaming default credentials -> google default credentials.
- Various other things in cpp:
  - Adding Cpp wrapping for JWT Tokens.
  - Renaming ComposeCredentials -> CompositeCredentials.

And reflects the C++ API in ServerBuilder.

Remove 'secure_serer_create', and instead attach credentials to ports, meaning different ports can serve different credentials.

- Tested with new tool (print_default_creds_token) on:
  - workstation for env var and well known place.
  - GCE for compute engine default creds.
- I'd prefer the grpc_default_credentials_create() API to remain
  synchronous even though there may be an async call for gce detection
  on which we block.

We have many assumptions about languages baked into the test system, and we want this test harness to trigger when testing C++ stuff, so it needs to be written in C++.

-) Secure files shouldn't be in the base grpc.
-) grpc++ depends on gpr.
-) grpc++ depends on protobuf (!)

This will help greatly when it comes to diagnosing customer issues.

- Makes 2 tests fail:
  - httpcli_test
  - interop_test

I'm honestly a little shocked this wasn't done previously.