Remove unused-variable in fbandroid/libraries/fbjni/cxx/lyra/lyra.cpp +3

Summary:
LLVM-15 has a warning `-Wunused-variable` which we treat as an error because it's so often diagnostic of a code issue. Unused variables can compromise readability or, worse, performance.

This diff either (a) removes an unused variable and, possibly, it's associated code or (b) qualifies the variable with `[[maybe_unused]]`.

#buildsonlynotests - Builds are sufficient

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Reviewed By: palmje

Differential Revision: D65755208

fbshipit-source-id: fca2b88ad04c554dca061d387e0eee40eae7f05e

cxx/fbjni/detail/Log.h

@@ -73,6 +73,8 @@ logassert(const char* tag, const char* msg, ARGS... args) noexcept {
   } while (0)
 #endif
 
+#define FBJNI_LOG_ONLY
+
 } // namespace log_
 } // namespace jni
 } // namespace facebook
@@ -83,4 +85,5 @@ logassert(const char* tag, const char* msg, ARGS... args) noexcept {
 #define FBJNI_LOGE(...) ((void)0)
 #define FBJNI_LOGF(...) (abort())
 #define FBJNI_ASSERT(cond) ((void)0)
+#define FBJNI_LOG_ONLY [[maybe_unused]]
 #endif

cxx/lyra/lyra.cpp

@@ -167,7 +167,7 @@ ostream& operator<<(ostream& out, const vector<StackTraceElement>& trace) {
 }
 
 void logStackTrace(const vector<StackTraceElement>& trace) {
-  auto i = 0;
+  FBJNI_LOG_ONLY int32_t i = 0;
   FBJNI_LOGE("Backtrace:");
   for (auto& elm : trace) {
     if (!elm.functionName().empty()) {