[presubmit] Enable runtime/threadsafe_fn linter checking.

src/base/platform/platform-linux.cc

Index: src/base/platform/platform-linux.cc
diff --git a/src/base/platform/platform-linux.cc b/src/base/platform/platform-linux.cc
index e2c321c07f09074aed4a49c0503b8e848c33ebbb..2a2abfeb25cf24ad0a3265405e1f10c6e5c2065a 100644
--- a/src/base/platform/platform-linux.cc
+++ b/src/base/platform/platform-linux.cc
@@ -108,7 +108,7 @@ const char* OS::LocalTimezone(double time, TimezoneCache* cache) {
 #else
   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 (!t || !t->tm_zone) return "";
   return t->tm_zone;
 #endif
@@ -121,7 +121,7 @@ double OS::LocalTimeOffset(TimezoneCache* cache) {
   return 0;
 #else
   time_t tv = time(NULL);
-  struct tm* t = localtime(&tv);
+  struct tm* t = localtime(&tv);  // NOLINT(runtime/threadsafe_fn)
   // tm_gmtoff includes any daylight savings offset, so subtract it.
   return static_cast<double>(t->tm_gmtoff * msPerSecond -
                              (t->tm_isdst > 0 ? 3600 * msPerSecond : 0));