Enable -Wshadow

Enable -Wshadow for upstream pigweed to improve compatibility with
projects that decide to enable this flag.

Change-Id: I7e1ce22f245e719ec78118370e591437abe07f0a
diff --git a/pw_tokenizer/base64_test.cc b/pw_tokenizer/base64_test.cc
index 4cf6b18..8a6f8b6 100644
--- a/pw_tokenizer/base64_test.cc
+++ b/pw_tokenizer/base64_test.cc
@@ -33,8 +33,8 @@
 
 const struct TestData {
   template <size_t kSize>
-  TestData(const char (&binary)[kSize], const char* base64)
-      : binary{as_bytes(span(binary, kSize - 1))}, base64(base64) {}
+  TestData(const char (&binary_data)[kSize], const char* base64_data)
+      : binary{as_bytes(span(binary_data, kSize - 1))}, base64(base64_data) {}
 
   span<const std::byte> binary;
   std::string_view base64;