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

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index 49916687696b4d6b05cf4caf524bc74ce7e3db25..4b87de5440a64c3a7647e5d55de2750944b55b18 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -3898,7 +3898,7 @@ HInstruction* HUnaryMathOperation::New(
       case kMathExp:
         return H_CONSTANT_DOUBLE(fast_exp(d));
       case kMathLog:
-        return H_CONSTANT_DOUBLE(log(d));
+        return H_CONSTANT_DOUBLE(std::log(d));
       case kMathSqrt:
         return H_CONSTANT_DOUBLE(fast_sqrt(d));
       case kMathPowHalf:
@@ -3911,9 +3911,9 @@ HInstruction* HUnaryMathOperation::New(
         // Doubles are represented as Significant * 2 ^ Exponent. If the
         // Exponent is not negative, the double value is already an integer.
         if (Double(d).Exponent() >= 0) return H_CONSTANT_DOUBLE(d);
-        return H_CONSTANT_DOUBLE(floor(d + 0.5));
+        return H_CONSTANT_DOUBLE(std::floor(d + 0.5));
       case kMathFloor:
-        return H_CONSTANT_DOUBLE(floor(d));
+        return H_CONSTANT_DOUBLE(std::floor(d));
       default:
         UNREACHABLE();
         break;