Discrepancy: String.data(using: .japaneseEUC) returns nil on non-Darwin.

[YOCKOW]

Given the following code:

import Foundation
print("Hello, world!".data(using: .japaneseEUC) as Any)

Results are:

OS	Swift	Result
macOS	5.10	"Optional(13 bytes)"
Ubuntu	5.10	"nil"
macOS	6.0	"Optional(13 bytes)"
Ubuntu	6.0	"nil"

This is not regression but discrepancy which should be also fixed.