Humor Kenton's NIH (use kj::inf() and kj::isNaN())

c++/src/capnp/compat/json.c++

@@ -20,7 +20,6 @@
 // THE SOFTWARE.
 
 #include "json.h"
-#include <cmath>
 #include <unordered_map>
 #include <kj/debug.h>
 
@@ -244,7 +243,7 @@ void JsonCodec::encode(DynamicValue::Reader input, Type type, JsonValue::Builder
     case schema::Type::FLOAT64:
       {
         double value = input.as<double>();
-        if (std::isinf(value) || std::isnan(value)) {
+        if (kj::inf() == value || -kj::inf() == value || kj::isNaN(value)) {
           // These values are not allowed in the JSON spec. Setting the field as null matches the
           // behavior of JSON.stringify in Firefox and Chrome.
           output.setNull();