[presubmit] Enable runtime/threadsafe_fn linter checking.

src/base/platform/platform-solaris.cc

Index: src/base/platform/platform-solaris.cc
diff --git a/src/base/platform/platform-solaris.cc b/src/base/platform/platform-solaris.cc
index e844aa12b486ed19e8c6657c3a79f1fefb41447e..7e07f1a1e2937e6c64f2a6a3880e3c6fa33e182b 100644
--- a/src/base/platform/platform-solaris.cc
+++ b/src/base/platform/platform-solaris.cc
@@ -38,7 +38,7 @@ namespace base {
 const char* OS::LocalTimezone(double time, TimezoneCache* cache) {
   if (std::isnan(time)) return "";
   time_t tv = static_cast<time_t>(std::floor(time/msPerSecond));
-  struct tm* t = localtime(&tv);
+  struct tm* t = localtime(&tv);  // NOLINT(runtime/threadsafe_fn)
   if (NULL == t) return "";
   return tzname[0];  // The location of the timezone string on Solaris.
 }