Use std:: on symbols declared in C++-style C headers.

src/platform-posix.cc

Index: src/platform-posix.cc
diff --git a/src/platform-posix.cc b/src/platform-posix.cc
index b8979308e3aee7e2eee4d3d10703e0d327ddcec7..3c62909b7513270e9191abe0613f871a967c6c61 100644
--- a/src/platform-posix.cc
+++ b/src/platform-posix.cc
@@ -296,7 +296,7 @@ void OS::DebugBreak() {
 // Math functions
 
 double modulo(double x, double y) {
-  return fmod(x, y);
+  return std::fmod(x, y);
 }
 
 
@@ -354,7 +354,7 @@ double OS::TimeCurrentMillis() {
 
 double OS::DaylightSavingsOffset(double time) {
   if (std::isnan(time)) return nan_value();
-  time_t tv = static_cast<time_t>(floor(time/msPerSecond));
+  time_t tv = static_cast<time_t>(std::floor(time/msPerSecond));
   struct tm* t = localtime(&tv);
   if (NULL == t) return nan_value();
   return t->tm_isdst > 0 ? 3600 * msPerSecond : 0;