Add XML & threading test files back to core-test target
Add XML & threading test files back to core-test target

They were removed earlier by accident.

JoyIfBam5/aws-sdk-cpp,awslabs/aws-sdk-cpp,JoyIfBam5/aws-sdk-cpp,cedral/aws-sdk-cpp,JoyIfBam5/aws-sdk-cpp,JoyIfBam5/aws-sdk-cpp,jt70471/aws-sdk-cpp,awslabs/aws-sdk-cpp,jt70471/aws-sdk-cpp,aws/aws-sdk-cpp,jt70471/aws-sdk-cpp,aws/aws-sdk-cpp,cedral/aws-sdk-cpp,JoyIfBam5/aws-sdk-cpp,aws/aws-sdk-cpp,cedral/aws-sdk-cpp,jt70471/aws-sdk-cpp,aws/aws-sdk-cpp,awslabs/aws-sdk-cpp,cedral/aws-sdk-cpp,cedral/aws-sdk-cpp,JoyIfBam5/aws-sdk-cpp,awslabs/aws-sdk-cpp,cedral/aws-sdk-cpp,aws/aws-sdk-cpp,jt70471/aws-sdk-cpp,jt70471/aws-sdk-cpp,aws/aws-sdk-cpp