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

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 3edea02a6f1483265a1ad4fc9b2f4fceb10e9dda..a7983ae586c5b3e6f3efbcd9e1b1b1d5a587e344 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1123,10 +1123,10 @@ void LCodeGen::DoMathFloorOfDiv(LMathFloorOfDiv* instr) {
     double multiplier_f =
         static_cast<double>(static_cast<uint64_t>(1) << shift) / divisor_abs;
     int64_t multiplier;
-    if (multiplier_f - floor(multiplier_f) < 0.5) {
-        multiplier = static_cast<int64_t>(floor(multiplier_f));
+    if (multiplier_f - std::floor(multiplier_f) < 0.5) {
+        multiplier = static_cast<int64_t>(std::floor(multiplier_f));
     } else {
-        multiplier = static_cast<int64_t>(floor(multiplier_f)) + 1;
+        multiplier = static_cast<int64_t>(std::floor(multiplier_f)) + 1;
     }
     // The multiplier is a uint32.
     ASSERT(multiplier > 0 &&