message: Look for `TEMP` and `TMP` env variables when returning the tmp dir path in tests
  These env variables are set on Windows.
diff: @@ -124,15 +124,18 @@ std::string HexEncode(absl::string_view bytes) {
  }
  std::string TmpDir() {
  - // The Bazel 'test' command sets TEST_TMPDIR.
  - const char* env = getenv("TEST_TMPDIR");
  + // Try the following environment variables in order:
  + // - TEST_TMPDIR: Set by `bazel test`.
  + // - TMPDIR: Set by some Tink tests.
  + // - TEMP, TMP: Set on Windows; they contain the tmp dir's path.
  + for (const std::string& tmp_env_variable :
  + {"TEST_TMPDIR", "TMPDIR", "TEMP", "TMP"}) {
  + const char* env = getenv(tmp_env_variable.c_str());
  if (env && env[0] != '\0') {
  return env;
  }
  - env = getenv("TMPDIR");
  - if (env && env[0] != '\0') {
  - return env;
  }
  + // Tmp dir on Linux/macOS.
  return "/tmp";
  }
  