Replace strptime with custom implementation (#5906)

* Replace strptime with custom implementation

* Fix ruby strptime

* Fix test

* Fix ruby conformance test

* Use mktime

* Remove EmptyFieldMask from failed conformance test list

Author: TeBoring

conformance/failure_list_ruby.txt

@@ -26,7 +26,6 @@ Required.Proto3.JsonInput.DoubleFieldMinPositiveValue.ProtobufOutput
 Required.Proto3.JsonInput.DoubleFieldNan.JsonOutput
 Required.Proto3.JsonInput.DurationMinValue.JsonOutput
 Required.Proto3.JsonInput.DurationRepeatedValue.JsonOutput
-Required.Proto3.JsonInput.EmptyFieldMask.JsonOutput
 Required.Proto3.JsonInput.FloatFieldInfinity.JsonOutput
 Required.Proto3.JsonInput.FloatFieldNan.JsonOutput
 Required.Proto3.JsonInput.FloatFieldNegativeInfinity.JsonOutput

conformance/failure_list_ruby_mac.txt

@@ -70,4 +70,3 @@ Required.Proto3.JsonInput.IgnoreUnknownJsonObject.ProtobufOutput
 Required.Proto3.JsonInput.IgnoreUnknownJsonString.ProtobufOutput
 Required.Proto3.JsonInput.IgnoreUnknownJsonTrue.ProtobufOutput
 Recommended.Proto3.JsonInput.FieldMaskInvalidCharacter
-Required.Proto3.JsonInput.EmptyFieldMask.JsonOutput