Patch from Firefox ESR 38 Void packaging.
--- mozilla/xpcom/ds/nsMathUtils.h.orig
+++ mozilla/xpcom/ds/nsMathUtils.h
@@ -104,12 +104,12 @@
 #ifdef WIN32
   // NOTE: '!!' casts an int to bool without spamming MSVC warning C4800.
   return !!_finite(aNum);
-#elif defined(XP_DARWIN)
+#elif defined(XP_DARWIN) || defined(_GLIBCXX_CMATH)
   // Darwin has deprecated |finite| and recommends |isfinite|. The former is
   // not present in the iOS SDK.
   return std::isfinite(aNum);
 #else
-  return finite(aNum);
+  return isfinite(aNum);
 #endif
 }