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

src/conversions-inl.h

Index: src/conversions-inl.h
diff --git a/src/conversions-inl.h b/src/conversions-inl.h
index 7ba19ba0f1d571657f51f68865dc24b700fc8ef3..3cb7ef29924ae1e7c058c65ef4a8fb5f3515d14b 100644
--- a/src/conversions-inl.h
+++ b/src/conversions-inl.h
@@ -88,7 +88,7 @@ inline unsigned int FastD2UI(double x) {
 inline double DoubleToInteger(double x) {
   if (std::isnan(x)) return 0;
   if (!std::isfinite(x) || x == 0) return x;
-  return (x >= 0) ? floor(x) : ceil(x);
+  return (x >= 0) ? std::floor(x) : std::ceil(x);
 }
 
 
@@ -233,7 +233,7 @@ double InternalStringToIntDouble(UnicodeCache* unicode_cache,
   }
 
   ASSERT(number != 0);
-  return ldexp(static_cast<double>(negative ? -number : number), exponent);
+  return std::ldexp(static_cast<double>(negative ? -number : number), exponent);
 }