Bug 1566697 - Fix unified build problem. r=longsonr

Differential Revision: https://phabricator.services.mozilla.com/D38262

--HG--
extra : moz-landing-system : lando

dom/svg/SVGPathData.cpp

@@ -167,7 +167,7 @@ bool SVGPathData::GetDistancesFromOriginToEndsOfVisibleSegments(
 
     // With degenerately large point coordinates, TraversePathSegment can fail
     // and end up producing NaNs.
-    if (!isfinite(state.length)) {
+    if (!std::isfinite(state.length)) {
       return false;
     }