[builtins] Unify Atanh, Cbrt and Expm1 as exports from flibm.

src/base/ieee754.h

Index: src/base/ieee754.h
diff --git a/src/base/ieee754.h b/src/base/ieee754.h
index 17034e50fcd24b05b5dc1f080a2f8145ba3c05af..ffb20734c0f3dbcca72bb6c3c8d068eef3112842 100644
--- a/src/base/ieee754.h
+++ b/src/base/ieee754.h
@@ -20,6 +20,8 @@ double atan2(double y, double x);
 // Returns the base-e exponential of |x|.
 double exp(double x);
 
+double atanh(double x);
+
 // Returns the natural logarithm of |x|.
 double log(double x);
 
@@ -33,6 +35,12 @@ double log2(double x);
 // Return the base 10 logarithm of |x|.
 double log10(double x);
 
+// Return cube root of |x|.
+double cbrt(double x);
+
+// Returns exp(x)-1, the exponential of |x| minus 1.
+double expm1(double x);
+
 }  // namespace ieee754
 }  // namespace base
 }  // namespace v8