Fix compiler warnings

Merge from Widevine repo of http://go/wvgerrit/43420

Remove or mark unused variables.  Fix unsigned/signed comparisons.

bug: 73390805
test: unit tests
Change-Id: Ic523400a5decf82fae733042b260e0c39a087cd3

libwvdrmengine/cdm/src/log.cpp

@@ -49,7 +49,7 @@ void Log(const char* file, const char* function, int line, LogPriority level,
   int len = snprintf(buf, LOG_BUF_SIZE, "[%s(%d):%s] ", filename, line,
                      function);
   if (len < 0) len = 0;
-  if (len < sizeof(buf)) {
+  if (static_cast<unsigned int>(len) < sizeof(buf)) {
     va_list ap;
     va_start(ap, format);
     vsnprintf(buf+len, LOG_BUF_SIZE-len, format, ap);